More memory will NEVER hurt in the long run.... It really depends on what you're doing.
As Duvie, Zebo and others can say better than I can, there are quirks with running 2 GB or more of RAM on A64. But the memory hits are pretty minimal.
I'm cutting over to contracting from full-time as of now and I can say I'm really f*cking glad I have 2 GB of RAM now (see sig). Though I can't run at 1T, it will still run rings around my old 3 Ghz P4 1 GB RAM work system. I had huge latency problems on that thing because I was running up to 30 tasks at a time. Now I'll get to make this thing sweat because I run Illustrator, FrameMaker, and many other apps during the course of my work....
Now I have to start thinking about an X2 4400+ because I might be able to justify it now for work....