I upgraded my mini to 1GB of RAM tonight. It is certainly more responsive during use, esp. when multitasking. I logged in and started FireFox, which opens the last 6 tabs I had open when it was closed. Then I switched users to my wife's account and started up FF there which opened the last site she was at. I left it running then I went back to my account and opened iTunes and started the latest H*R podcast and left that running. Then I went to FF, went to Google Video and watched a streaming video. Switched back and forth to iTunes and FF and no hiccups. Butter smooth. Running Tiger is really great at 1GB. Heck even the 640MB in my iBook is smoother than the 512MB that was in the mini (smoother, not faster). Now I'll have to see if doing a DVD rip goes faster at all.
And to top it all off, the 1GB of Viking OEM'd Elixir RAM was still in a sealed AS bag. NIB from a nice guy on Craigslist, and I got it for only $35! I'm very happy. A quick search of the particular module online shows $120-ish to $140-ish! My P4 Linux machine went to 1GB too, with the extra 512MB DIMM from the mini.