Good for age guarantees a place (only for UK runners)
Charities will grant you a place if you pledge to raise a set amount (was £1,500 but may now be £2,000) I don't know how strict this requirement is as I've never entered this way.
The ballot chances are not great, but I'd say more like 1 in 6 or 7. I've got a 3 in 9 record.
The ballot is not first-come-first-served, so getting in early has no effect. there is a closing date though, so make sure you apply before then.
There are various theories regarding how the information you supply when you enter increases/decreases your chances. I think the official line is it has no effect, but I'll let someone else comment if they think differently.
Hope this helps!
Edited: 13/04/2011 at 13:29