I have a mac mini 1.25 with 512 of ram, and it runs WoW ok soloing, but you can't raid, and big cities are difficult.
In 800 x 600, FPS are around 25 outside with everything turned off. It usually varies massively though, dropping down to around 10 most of the time.
So, i'm trying to say 25 fps isn't solid, more of a lucky spike!
Edit: I'm upgrading to a G5 iMac soon, and I'm going to stick 1gig ram stick in there, bringing it up to 1.5. If I wasn't, I would consider buying a gig of ram for the mac mini, but I can't see it making much difference.