[Christof]

I'm thinking about picking up a new iMac for my gallery.  There will be three individuals who use the computer.  Myself for audio/photoshop/Sketchup, my girlfriend for basically the same and our receptionist for keeping records/office work. 

I would like to know if creating 3 separate user accounts will effect the performance of the computer?  If so, should I take this into consideration when ordering and what should I be looking for in terms of upgrading?

Here is what I'm looking at: http://store.apple.com/us/configure/MC509LL/A?mco=MTg1ODA4MDE 

[skunark]

It's generally not an issue but you have two options to enable multiple users: 

1) If you enable fast switching between users then you might want to plan 1-2GB of RAM per user that you would want to be logged in and running applications at once.   The mail, browser and basic office applications will easily consume 1GB of RAM and these would just push to the background when switching users.   But not all applications will push to the background when switching, for example games and video editing for example and instead of increase the memory, just discourage fast switching during those times.   

2)If you don't enable fast switching between users, meaning users have to logout before the next can login, then 4GB is plenty for most users, otherwise for the extra $200, it might be worth having the 8GB.   Historically memory prices drop drastically so you might wait on upgrading from 4GB to 8GB until you know that you need it.

If i had an extra $200 to spend on options today, I would probably snag the core i5 over the i3 and add more memory later.