I haven't seen any info on how many applied for the ballot this year, but apparently it was nearly 100,000 last year.
Artemis - if you're thinking of running it one day, put in an application next year. It's unlikely you'll get in first time anyway. If you do, then you'll hear early December, giving 4 months training, which should be enough if you've been running regularly before then.
If you don't get in, and are unlucky for a few years then 5 rejections in a row means you definitely get in 6th time. So if you start next year you'll definitely get a place by 2012 at the latest! (That could be a popular one being Olympic year!!!)