I got along for several years with just 1 GB in my Mac mini, but by the time Snow Leopard came out it was just not enough RAM to run all the apps I like to have open at the same time. So I upgraded to a MacBook Pro with 4 GB of RAM and thought I'd be set for a long time.
Now I'm running all my regular apps, plus Parallels for a Windows 7 virtual machine to run all my work software, and 4 GB is feeling pretty cramped. I'm starting to see the Spinning Pizza Wheel of Death more and more often, and it's getting a little frustrating.
I've thought about bumping up to 8 GB of RAM, but that's almost $500 and I can't really justify that right now. Sigh. Where's RamDoubler when you need it?
ETA: Sorry about the cruddy formatting and lack of title for this post earlier; I was trying TypePad's new quick compose option and, obviously, the result's aren't grand.