Yeah theres a little performance drop, depending if you configure its CPU usage to idle or low priority. I always set it to low and experience no noticable performance drop when browsing the web or orther menial tasks. But SuperPi tests confirm around 30-40% increase in calculation times. Memory usage is usually pretty high with the SMP client so if you have a software running that is sensitive to high memory demands (like my video surveillance server running DVR software) folding may not work on that machine.
On a side note, I was wondering if anyone had some information about the NvNews / OSNN / SP merger. Did the teams merge, combining points or did some members have to abandon their old team number for one of the others, with a team name change? Reason I ask, my 'old' team is going through restructuring since abit is R.I.P. but we have a jackass running the show who doesn't want to change the team name (because of his username), even though we had a team of a handfull join up. The majority of the team wants a name that better describes us, 'United' something-or-other to better encompass multiple teams under the same flag. I just wanted to know if it's possible to combine teams in a neater way than giving up on a particular team number altogether, and forcing the new join-ups to start over from zero.