I'm doing alright so far... Only been doing it about 3 weeks and just last night added enough to get me to 1.5 Gh/s.  New cards bought on sale with rebates and selling game cards brings the cost way down.  Installing them in a handful of systems I had laying around- I've brought in about $140 for $700 in expense so far.

I'm having fun, and it looks like I'm going to do alright- no it won't make me rich, but especially when it comes time to sell cards I think I'll come out ahead by a fair bit.

PS- I did pre-order a BFL Jalapeno a 6 weeks ago.