League-of-legends – How many Krakens do you earn in black market brawlers

[Y]ou will be able to purchase up to seven additional runes pages for a grand total of nine.

— Additional Rune Pages Available for Purchase!

9 - 7 = 2 for new accounts

QED

It seems like Riot has used the promise of a free rune page to motivate their players to go vote or participate in this or that. Presumably everyone who had an account prior to then would have a bonus one for free.

[Updated for Season 3]

The game is currently in flux (season 3 has only been out for a couple days), but with the boosted ambient gold gain, it appears you only need one gp/10. I've been building Philo Stone to great success. If you expect to get some significant assist-gold (you're confident in your kill lane, or you're Soraka and have a good eye for your ultimate), you could probably stand to buy a Kage's Lucky Pick, but I much prefer to only buy the one Philo Stone and start immediately after into my build (Sightstone, Shurelya's, Aegis -> Bulwark).

Again though, this is all pretty fresh. Your mileage may vary.

[NOTE: The answer below was provided for season 2. There were significant changes implemented for Season 3, and this answer is now out of date. It is provided here for history, but should not be followed.]

It depends. The rule of thumb is two (Philo Stone and Heart of Gold), and 98.355% of the games, you'll want those. If the game is going to absolute crap, teamfights started early and your team is getting routed, you may have to skip the second and start pouring that extra money into wards and an oracle's (counter to what you'd think, oracle's is a great purchase if you're falling behind and the laning phase is over).

I'd be very suspicious of my support if they got a third gp/5. The only real time I can see that being worthwhile is if you know it'll be a late, late game, and that you'll need to be a significant contributor in teamfights for damage.