Nidalee is an AP support, but can be played as a carry due to her OP cougar form and spears. Her spear is a skillshot nuke that can deal up to 2.5x more damage the farther away you throw it as you all are aware of. Her ultimate is the mighty cougar, in this form she gains movement speed, armor, and magic resist. She also gains mana-free skills with very low cooldowns. The W pounce can be used every 3 seconds, and can be used to hop over walls to either escape or chase. Her cougar, pounce, and her passive 15% extra movement speed combined with the lichbane makes her a very difficult girl to catch or escape from.

The deathcap is for Nidalee's AP spells. The deathcap will make her spears a huge nuke. The lichbane will stack with her cougar Q(since the Q is an on-hit attack) dealing damage equal to the Q itself with your current AP. At this point you should have the rabadons making it deal an additional 300-ish. Nidalee is a very mana-spending champion as all of her skills cost around 100 mana. Getting the grail will ensure that if you spear someone in the head, you will get a good return of mana to move onto your next target. The rylais will make your tanky and slow anyone you hit. So if you spear someone, the rylais will slow them and then you may switch to cougar form for the kill. The void staff will ensure that your spears are hitting for a great deal of damage regardless of magic resist.

For teamfights, you should stay back and chuck spears at their carries and heal your own carries BEFORE they actually start to take damage, the speed buff from the heal will allow them to dish out more damage, and whats the point of the speed buff if you use it after the fights over? Change into cougar form to chase down the people who flee from battle and the remaining people from the teamfights. Make sure you use traps to ward baron, dragon, and your/their jungle. Nidalee's spear will do damage based on how far you are when they hit. So if you throw the spear and run the opposite direction, it will do more damage. in Siv HD's Nidalee guide, he throws the javelin spear and then flashes the other direction ensuring the spear will do maximum damage.

Pros
Nimble
Can be played AP/AD
Spears have long range and massive damage
Heal increases attack speed and heals for alot
Traps act as wards and lower armor/MR
Can jump over walls
Cons
Spears are slow and easily dodgable
Spears are blocked by minions
Heal has a long cooldown
if you miss the hop your ****ed

Nidalee is an excellent farmer. Her cougar pounce and E scratch will wipe out minion waves instantly, the speed buff from her heal also allows her to last hit like a champ. Her traps are actually AOE as well, so they will hit multiple targets inside the trap.