Sorry to bring this back on topic; I use a MBP 15 (Mid 2008 one, 4GB RAM) along with a 23" ACD. It easily outpaces a colleagues Dual G5 2.5. For instance on one project we run a set of specs, MBP: 90seconds, G5:4 minutes.
Unless I found myself doing lots of HD video day-in-day-out (and lets face it, I'm a programmer most of the time, so not likely to happen soon), then I would get a Mac Pro, but the Core2Duos are more than powerful enough for almost any other media workload.
MBPs rumoured to be getting matte screen option for the 15" in September, so I'm waiting till that happens before replacing this one.