Sometimes, something causes the CPU to peg, thus firing up the fan to maximum. A few do this on my Macbook. Sometimes it's Safari (though that dies down after awhile), sometimes it's iCal (which launches this process called SyncServer which pegs the CPU and thus the fan..annoying.)
Usually when Safari does it, it's because I'm on YouTube, and Flash player seems to want to take up as much CPU as it can get. Closing the tab usually calms the fan down. iCal regularly launches that SyncServer which uselessly takes up CPU and gets the fan to max. I kill SyncServer in Activity Monitor and it stops doing that.
Annoying, more than anything. I haven't found anything on the 'net yet which explains why SyncServer decides to go nuts, however. Perhaps your printer driver is one of those.
Another one is this Checkpoint SecureClient VPN client which is used by my employer. I install that so I can maybe access my employer's servers remotely. It insists on rebooting my Mac after installation (which is the first indication that this is screwed-up software) and then proceeds to take over as much CPU as it can. So I deep-six that by uninstalling it and that problem goes away. Still leaves me unable to use my Mac to do employer-like things, but not a big deal, since they've provided me with a really crappy, but functional Windows machine.
Anyway, some software, while being useful in design, sometimes hasn't been fully tested sufficiently to work in the Mac world.
