Three words: BUY MORE RAM!

[strobe]

OS X will use every byte of RAM you have. If not for anything else the remainder is used as disc cache. This speeds lots of things up like doing another complex search in Sherlock, or relaunching an application, or using Classic applications.

RAM is very cheap right now. I got a 256MBPC100 CAS2 SODIMM for a Pismo for $100!

I bet even the lowliest iMac will run OS X well if it has lots of RAM. I'm really tempted to double the amount in my G4 450 to 512MB.

[endian]

I've been tempted to max mine out at 1.5GB, but for some reason I've been itching to get a flat panel display lately...

And yes, RAM does make a huge difference. (just to stay on topic

[kenaroni]

I'll agree here...
Previousy I was running OSX on a G4 tower with 128mb total ram. OSX ran ok, but Classic was a dog. Now I just added another 128mb for a total of 256, and Classic soars! I was running Dreamweaver and Photoshop at once in Classic, plus Internet Explorer and Audion in OSX. The Classic apps were running smooth and fast. Of course I'd rather have enough OSX apps so I would never have to bother with Classic again.