No, it isn't too big. 21" monitors (particularly trinitron/diamondtron ones) are wonderful. They may look big for a couple hours, but you will get used to it REALLY fast. I recently switched to an 18.1" LCD 1280X1024 flat panel, which in viewable area, is a bit larger than your average 19" monitor. While I can't say that I really "miss" the extra size of the 21" monitor, I think that bigger in a monitor is always better. That said, I am not at all sorry I switched. 1-2" of viewable area smaller for being able to stare at it for HOURS and HOURS without your eyes ever getting tired is a very good trade. Consider a flat panel if you can come up with the ca$h (or find a deal like I did).
Nack