My Dell Inspiron 6000 with WXGA came with only 256MB of memory, which was fine for what I was going to use it for. Lately, though, I've had a need to run Visual Studio .NET, which is a resource intensive development environment.
As an example, the Task Manager currently lists devenv.exe as using 156MB of memory and 99MB of VM.
I was loathing the slow performance and constant paging, which were made all the worse by having Firefox (lately somewhat of a hog itself) and iTunes open.
I ordered a $38 stick of G.SKILL 512 MB DDR2 to try and remedy the problem. I originally aimed for another 256, but the 512 was like $6 more.
The difference in Visual Studio's performance is amazing. Microsoft's hardware requirements list 192 as the minimum, with 256 recommended. I really can't see going below 512.
Nothing new here. Memory is cheap and is the best upgrade you can usually make for a system.