If you know what I mean... ;D

So far, my best score is 15/2/11.
Second best is 10/5/14.

Here's my guide on how to play the "underpowered" Caitlyn.

In my opinion, she is very balanced, at least. She does great in middle lane and side lanes. Shes practically ungankable with her Yordle Snap Traps and 90 Caliber Net. Her Piltover Peacemaker is an excellent harasser with great damage and range. And even though her Ace in the Hole's range is surprisingly low, it scales amazingly well. 300 additional attack damage will put it well over 1,000 physical damage at rank 3. Who would want to tank that for a teammate? Her two damage dealing skills both deal physical damage, which is why this build focuses on armor penetration.

Since MOBA doesn't have the damage and scaling yet, I'll put them here:
Q - Piltover Peacemaker - Deals 40/70/100/130/160 + 100% of attack damage as physical damage.
W - Yordle Snap Trap - Deals 80/130/180/230/280 + 60% of ability power as magic damage.
E - 90 Caliber Net - Deals 80/130/180/230/280 + 80% of ability power as magic damage.
R - Ace in the Hole - Deals 250/400/550 + 200% of bonus attack damage (any attack damage that isn't base damage) as physical damage.

Greater Mark of Attack Damage - For the early game. With a Doran's Blade, her Piltover Peacemaker will do 110 damage. And her auto will do 70.
Greater Seal of Scaling Mana Regeneration - These, combined with the Meditation mastery, solve her mana issues.
Greater Glyph of Scaling Magic Resist - These are replaceable. I hate going against casters so I get these haha. Other glyphs you can get are Greater Glyph of Mana, Greater Glyph of Cooldown Reduction, or Greater Glyph of Scaling Mana Regeneration.
Greater Quintessence of Desolation - Armor penetration. You're gonna need it.

Boots of Swiftness - Pretty self-explanatory.
Black Cleaver - With the recent changes, this is perfect for Caitlyn. Attack speed procs Headshot faster, attack damage for her Q and R, and armor penetration :D
Black Cleaver - Get two of dese suckas.
Sword of the Occult - I admit, it might be hard to get kills when everyone is running away from you, but you'll manage. And once you get full stacks, you can easily catch them ;D
Youmuu's Ghostblade - Armor penetration, attack damage, and some critical chance couldn't hurt. And if you're 1v1-ing someone, just activate it and watch all the Headshots.
Banshee's Veil - Just a general defensive item. If they aren't caster-heavy, of course get something else with armor, or just health (like a Frozen Mallet).

Piltover Peacemaker - Focus on leveling this first. I always take this first, unless we have a jungler, in which case I get Yordle Snap Trap to protect them. Whenever this is available, level it.
Yordle Snap Trap - Usually my second, if not first, skill. Use it to put in river bushes to prevent ganks. Or if your opponent likes to come at you, just put them on the ground, between minions, where its hard to see. Max this second.
90 Caliber Net - I really just take one rank of this at level 4. You're not going AP, so the damage doesn't matter at all. The utility is the same no matter the rank. Focus this last.
Ace in the Hole - Of course, get this at levels 6,11,16. I don't use it in teamfights. Its too hard to even snipe with everyone in the way. I found that if you stand to the side of team fights, and lay an escape path with Yordle Snap Traps, you can easily escape anything, and it gives you a better angle to snipe if anyone runs away. And if they focus you, they'll get trapped and your team will just chase them while they're preoccupied.

Personally:

Ghost - I don't think Ghost is ever not a good spell to get.
Exhaust - Due to the recent buff, this has saved my life so many times.

Recommended:

Clairvoyance - Always a good spell to get. It works well with Ace in the Hole in case they're in jungle, over a wall, or just out of range. Also snipe a Warwick soloing Baron if you don't have a ward :D
Flash - Sometimes I've tried to 90 Caliber Net over a wall, but I couldn't for some reason :/ That's where this comes in haha
Cleanse - Dem *****es always be tryin' ta put dat crowd ****roll on meh.

Maybe:

Teleport - Good to return to a lane after a recall. Good to go to another lane to gank.
Ignite - I personally don't like this spell. Especially since you shouldn't be getting close enough to use it.

Nope:

Heal - All of these just aren't as useful as the ones above. And can be easily avoided using.
Revive - All of these just aren't as useful as the ones above. And can be easily avoided using.
Smite - All of these just aren't as useful as the ones above. And can be easily avoided using.
Fortify - All of these just aren't as useful as the ones above. And can be easily avoided using.
Clarity - All of these just aren't as useful as the ones above. And can be easily avoided using.
Rally - All of these just aren't as useful as the ones above. And can be easily avoided using.

Just thought I'd put this in here.

I've been trying to jungle with Caitlyn, and have had some success with it.
My general route is Blue Buff > Wolf Camp > Wraiths > Golems > RECALL > Lizard > GANK
- The bushes by the Wraiths and Golems are just close enough to attack without losing agro.
My spells were Ghost and Smite.
My masteries were... 15/6/9 I believe.
My runes were Greater Mark of Desolation, Greater Seal of Armor, Greater Glyph of Scaling Mana Regeneration, and Greater Quintessence of Health.
Started off with a Cloth Armor and 5x Health Potions. Turn Cloth Armor into Madred's Razors, then get boots next time.
Skill sequence was Piltover Peacemaker > Yordle Snap Trap > Piltover Peacemaker > 90 Caliber Net.

It would be a lot easier if you started jungling at level 2. And maybe Greater Mark of Critical Chance would work better with her passive. Crits + 250% damage.