The magic number is 350000. Nice and round number.
If we have that many total peers on Monday 16th of May, when the European staffers have woken up some hours after the freeleech period has ended, we will guarantee another leechfest within the next two months. This means that we're aiming to double our peer amount within a week. It's doable but tough. You can follow our progress from the statistics part of the front page. It's "Peers" under "Peer Statistics". Those numbers are updated once a day.
In case of any questions about or troubles during the leechfest, consult the forums, ask for help on IRC
or contact Daeron directly.