I added 512 MB of PC2700, IBM branded RAM into my 1 GHz 17" powerbook running panther. It ran fine and I later sold it to a friend and bought a 1.67 GHz 15" model. By then RAM had dropped in price and I bought from crucial in order to upgrade my new model.
Months later, my friend upgraded to tiger and the thing started running like crap with lock-ups and application quits many times per day. Coming from the windows world, she thought it was just business as usual and that Mac tales of reliability were exaggeration! Now, I'm pretty good with Macs and can normally solve issues quite quickly. I'm first port of call for most of my friends with computer issues, be they Mac, Linux or even windows, but I couldn't get that powerbook to run anything newer than panther, no matter what. Also, by then she had moved to a different city, so my opportunities for solving her problems were limited to her occasional visits.
Eventually, I found references to the 17" powerbooks RAM fussiness on Apple's support site and we swapped sticks between her powerbook and mine. That was last weekend and we tried an archive and install of leopard. It went on with no problems and is now rock solid. Also, my 1.67 GHz seems quite happy with the IBM RAM, although it doesn't get much use these days, only when I need a second laptop for a gig.
Well, that was longer than I intended but here it is in a nutshell. You should be aware that non-compliant RAM is a particular problem in the 17" models and that problems can occur months later, rather than being immediately apparent.
