Talon currently is very overpowered. He bursts for high damage and his abilities are low cooldown. However a lot of kids are currently screaming that he is very underpowered.
Mainly I believe this is because people are not building him straight AD, going for items such as brutalizer instead of a BF sword, which is similar to being told to build straight AP and building a Fiendish Codex rather than a Needlessly Large Rod and hurting your build.
Another problem is I see people rushing Sheen, which is a redundant item and a waste of money as Talon has no use for AP, which is sad because we have to waste a mastery in Archangels Savvy unless you prefer to use Exhaust over Ignite, which is very viable due to the 10% extra damage passive on slowed targets.

Last two matchs:

Pros:

Huge Burst
Low Mana Cost
Low Cooldown
Amazing Ultimate
Very good late game
Good farm and last hits nicely

Cons:

Glass Cannon
No great escape other than your Ult, and Flash
****ty early game
Mid game after burst can leave you vunerable
Gets gibbed in team fights if you are not careful

I tend to mix and match my runes a lot, but I don't like to give up too much to survivalibility. Currently I choose Standard AD Champ runes. I don't see that much of a need for Health Regen Quints or Straight MR Glyphs. So i take MR/lvl Glyphs instead and an offensive Quint, in my case i choose Furor Quints for a cheeky extra bit of Crit Dmg.

If you use Exhaust, use Cripple rather than the useless Archangels Savvy.
Other than that I take 21/9/0, because I prefer Nimbleness and the extra protection to the useless 9 points which at best provides me with a little experience increase. Of course, you may prefer this, I have no problem outleveling people with 21/9/0.

Early Game:
Start with a Doran's Sheild. It will keep you in lane a lot longer than most items and will allow you to farm enough to go back for your Beserkers Greaves. Obviously if they have high CC on their team, switch Beserkers Greaves for Mercurys Threads, Attack Speed isn't that important on you in comparison to other AD champions so if in doubt, get Mercs.

Next time you go back get a B.F sword, this will give you enough damage to participate in a duo lane fight. However you won't be doing much damage untill you get your Bloodthirster.
Once you get your Bloodthirster, fill it with as many stacks as quickly as possible with minion kills. Make sure to help get dragon, as he will help a lot with your expensive build.

Mid Game:
Infinity Edge/Phantom Dancer is when you start changing the game in your favour. The damage from this combo on any AD carry is amazing, and on top of your 100AD from your Bloodthirster, you will be hitting for stink loads and be able to follow up after your burst, chasing down to poor people who didnt die during it.

Late Game:
And it doesn't stop there, Frozen Mallet/Atma's Impaler. This provides you with a stink load of offtankiness, but not forgetting, the permaslow from FM giving you a constant 10% extra damage from your passive. And not only that, but your Atma's Impaler, gives you an extra 50+ damage as well as the Armor and Critical Chance.

Situational:
Of course, this is the perfect build, but things are never perfect. If you find yourself getting focused, you may need to swap the Atmas Impaler and purchase a tank item early, such as a Banshees Veil, Guardian Angel, Thornmail etc.
Just remember that you are a late game carry, if you are 0/3 at level 8 in a normal game, you will most likely be 13/5 late game.

Triforce

Theres no lying that in theory this gives a little of everything that benefits Mr. Talon.
However:

It doesn't provide enough damage.
Sheen's AP is a wasted stat.
Frozen Mallet is a core item due to its permaslow and permabuff for talon.
Phantom Dancer synergizes better with Infinity Edge than triforce.

Rushing Triforce is too expensive to get instead of other items early that would provide more straight AD damage and burst.

Brutalizer/Youmuus

Talon is a burst champion, meaning you want as much straight AD early as possible.
Talon is similar to the AP champion LeBlanc, who I believe should be built straight AP. Buying a Brutalizer/Youmuus instead of rushing a Bloodthirster on Talon is like getting a Fiendish Codex/Morellos Evil Tome instead of rushing a Deathcap on LeBlanc, which in the end will provide benefits, but will hurt your burst bigtime which is where Talon is strongest.

Fatmogs

Fatmogs/Atmogs is a generic AD build for champions that should be carries, but need to play offtank for whatever reason (bad team comp). It's viable but requires a lot of farm. Only situation I would build something like this is if I had a Sword of the Occult as I will receive enough damage from my stacks, as well as being able to keep them due to the tankiness of Fatmogs. This means you would need to have had a very good early game. However a Madreds Bloodrazer or KogMaw can destroy HP tanks in seconds so be carefull


Double Bloodthirsters

A very common build for Sivir, as well as triple bloodthirsters due to her ridiculous farming abilities, allowing her to stack crazy amounts of damage extremely quickly. In your case though you do not farm as quickly. However, if you are doing well and not dying too often, you could always swap out Atmas Impaler for a second Bloodthirster. I wouldn't get it untill after my critical items (IE/PD)

Double Phantom Dancers

Doesn't provide extra damage to your burst, however it will benefit the items you already have and make your followup just as good as your burst in end game.

Mercy: A nice passive, especially on a team with a lot of CC. If you manage to make it to your Frozen Mallet, the synergize very well and will let of pick of targets you missed.

Noxian Diplomacy: I see no reason why not to max this first, or max it alongside Rake, other than I prefer to use as much of the early game to harass and last hit. Noxian Diplomacy should be used last in your burst and spammed untill the enemy is dead. Since its mostly used in your burst sequence, which is effective later game, you may as well wait untill after Rake is mastered.

Rake: Your best farming and harass tool. Provides a neat slow to synergize with your Passive. Probably your best ability early game and should be the first skill you pick.

Cutthroat: Practically Shunpo with a silence and debuff instead of damage minus the ability to hop to allied targets. Necessary for your Burst so stick a point in this at level 2 or 3. Master last.

Shadow Assault: Huge amount of damage covering a large radius while also stealthing you and giving you a huge movement speed buff and its on very low cooldown.

Burst Sequence [Flash>Cutthroat>Rake>Shaddow Assault>Noxian Diplomacy>If enemy is low, Autoattack and spam Noxian Diplomacy; otherwise escape]

Flash is absolutely necessary on Talon.

Ignite/Exhaust
Its a head and tails toss between exhaust and ignite, ignite can gaurantee kills while exhaust added to your burst will make your passive more constant.

http://www.youtube.com/watch?v=gvdf5n-zI14

Best of luck, and if you have any questions or reccomendations, let me know.

Changelog:
08/25/11 Uploaded.
08/26/11 Added Pros/Cons