Yes
I never shut my iMac down, it's running 24/7 as im always doing something. It Just goes to sleep if there is any inactivity. Id imagine there's also quite a large amount of people here who do this also.
There is an argument about if it uses more power keeping on 24/7 rather then shutting down/starting up.
The OS counts on your iMac being left on in order to perform daily, weekly, and monthly tasks.
i have a very noob question: if the computer goes to sleep, can you access it remotely? use it as a server? etc etc
I have a late 2007 iMac 2.4 at work, and I leave it on 24/7 and set to never sleep (the hard disk and screen both sleep however). I have not had any issues with it. It does the normal hourly time machine backups and weekly SuperDuper! backups to a locally attached usb hdd.
Set one of the corners as "sleep display" corner, and when you walk away just move the mouse to that corner.
I find that 5 min of inactivity to sleep display isnt enough sometimes I dont like wiggling the mouse to make sure. And 10 min is too long to sleep when I walk away. Also, dim before sleep comes on far too quickly for my tastes. So, to the corner it goes.