I had an old g4 mac (800mhz, 1gb ram) with OSX kicking about under the stairs. With it's flatscreen it was origionally for the kids to potter about on, but they weren't interested. I landed a wee pc laptop for them and the wife to use but had this big mac left doing nothing.
Now I RDC from work to home daily to chat on the IRC channel with ma homies, but that was onto my dual core gaming rig. Seemed daft to wear that machine out, so I popped the mac in the downstairs cupboard with the boiler.
Now Apple remote desktop is a bastardised version of VNC, it's slow and shitty. However vineserver is actually quite neat, it runs as a service and has been rock solid for a month or more now. Connect to vineserver with the usual VNC listening app.
I've still to configure ssh on that mac actually, must get onto that.
Once I set the res to 1024 I popped the screen off and put a vga cable in, that lets it run headless as well. Anyone else wanting to do this change your dock settings so that the swirly thing doesn't happen. Thats a proper PITA. minimize using scale effect and untick animate opening applications
For grabbing linux distros (ha) azureus works fine, a bit slow but transfer rate is actually faster than the pc upstairs quite often.
IRC was a problem, I used colloquy. That was slow as a week in the jail at rendering the conversation. I moved to X-Chat Aqua and thats the dogs, light n fast it's working superbly.
thunderbird and firefox handle web and email really well. It's also handling the sharing of media to my xbox with xbmc over SMB without any problem either.
Putting the mac to sleep is a godsend too, I can log into my router over https on a specified port and issue a Wake on Lan instruction the mac and it pops up ready for akshun.
As I say, I've been using it for a month or so now and it's a big boost to passing the time at work ;) Plus as it's only got 1 hard disk, it'll probaby consume less power than the beast upstairs (which has 3). Hear me Al, I'm saving the world too!