Purchasing an iMac: when is the entry-level model insufficient? We're looking at iMacs for my girlfriend, and I was wondering: would the entry-level model be sufficient?

When looking at Windows desktops, I tend to suggest a model a few levels above an entry-level desktop. This usually means the PC can be used longer and it will feel like a fast desktop for a while longer.

Is the same true for an iMac? When is the basic model insufficient? Naturally, this is not a $300 PC, so I would think that even the basic model is a very capable machine. However, for only a few hundred dollars above the entry-level model, CPU speeds are doubled, among other improvements.

Again, this is for my girlfriend, and she really only uses it for internet, the occasional movie and listening to music.
It depends on what you / your girlfriend wants to do with the iMac. If it is really just used for internet and occasionally watching a movie and listening to music, then an 'entry level' iMac offers more than enough performance. IMHO even an iPad would provide enough performance…

We actually use our 5+yr old iMac (Intel Core 2 Duo, 2.66GHz) as a media hub and it works just fine. It's connected to the TV and has a couple of external hard drives connected to it. And when it got a bit slow a couple of years ago we just added some memory, both RAM and HD, and that really helped a lot. Now it's basically never  

Also all other apps like Photoshop etc. still work fine on that machine, but since we now have some faster machines in the house, the iMac is basically just used as a media hub.