Lulu is a mighty fine kiter, and I'd like to talk a little about the utility of her abilities early game and how she can build into a broader role than one that can be described as just 'Support' or 'Caster'

You'll see a key component of Lulus early build and runes/masteries is Gold/5. This is because her abilities are not aimed at giving her a good creep score (until her Glitterlance is levelled at least). She would do much better to allow a ranged carry to farm minions and support them with Hey Pix (both shielding/protecting them and making use of Pix' reliance on AS)

A little defence and sustain is dabbled in, (of course you can tailor this to how 'manic' you play her) but a key component is MPen, which you would usually avoid on some other supports. This is tailored to give Lulu some punch when she starts to harrass enemies, as Glitterlance, Hey Pix and Whimsy combine to a lethal set of skills which can keep enemies at arms length.

Pros

Her heal and shield combine to save people from any fight unless they are focused by multiple team members
Hey Pix effectively doubles Lulus offensive range, meaning she can stay WELL out of the fight.
She has 2 CCs for escape, Whimsy, Hey Pix (to extend range) then Glitterlance (in direction enemy is running) can save you from most chasers.

Cons

If whimsy is on cooldown, you can be caught up by ghost or flash.
Pretty useless in a big teamfight compared to most other supports

What does lulu have more than anyone? The ability to get someone into a fight, and give them a defensive and offensive advantage OR the ability to keep enemies at arms length in a chase / fight. I even heard that Sivir was a counter, but a Sivir with Ulti, Zeal and Boots (plus other items) was kept at bay in a 1-on-1 at level 12 until an AD carry came to finish her off quickly (-75% health in comparison to my -25%).

HEY PIX, GLITTERLANCE = SLOW at HUGE RANGE
WHIMSY = SLOW/SILENCE or SPEEDBOOST

Need I say more?