Remember that Steam is available on Mac and their library gets updated quite often. I'm afraid I don't have any suggestions at the second though as I haven't played Geometry Wars. Give me a few minutes to go and look it up.
EDIT: Ok, so I checked out some gameplay footage...how you're able to play that and pay attention to a podcast is beyond me.
Anyway, that's not normally my gaming style, at least not on my Mac, so I don't have any real suggestions for a similar game. But Peggle comes to mind as similar in that you can pick it up for a few minutes and then put it down, and there are quite a few games that have the same arcadey feel to them. Check out Steam's Mac section
and see if something takes your fancy. The smaller indie games would offer you something to pass the time without having to do major gaming sessions.