Even most people running ASICs still use pools. It's just a way to reduce your variance.
The prospect of mining a 25BTC block and suddenly becoming $2,500 richer in one minute is tantalizing. However, it's damn near impossible.
From
http://www.bitcoinx.com/profit/ for 1.2GH/s at the current difficulty:
Average generation time for a block (solo) - 1 year, 98 days (can vary greatly depending on your luck)
And this number is only going to get higher as the difficulty goes up.