Temp

Depends on what you're doing (which programs you run). And which temperature you're talking about. All these are CPU bottomside:

A few, light programs should give you a temp in around 45-48°C (113-118°F).

Run Safari in several tabs (with some flash contents) and/or AirTunes, and you will quickly see 55-58°C (131-136°F).

Some heavy work, like ripping CDs, playing games and/or running Classic applications, should bring you up in 65-67°C (149-152°F) at which point the fans should kick in and (hopefully) bring you down to around 60°C (140°F).

And, just a tip at the end, this question has been answered more than once on these forums already...