I got this bag with the intention of future expansion. It's a good size; my girlfriend commented about how good my "man bag" looks. I only have a 450D and 17-50 Tamron at the moment, but I'll be getting a 70-200 and 1 or 2 more prime lenses later. This should fit all of those well. I don't think it'll fit a flash as well, but it should be able to hold 2 lenses plus a flash easily. I like the extra pockets to hold cleaning tools and extra batteries/memory cards. My only current caveat is the excess on the velcro with the buckle for the main flap. I can see this as a good security deterrent, but otherwise it can be a nuisance. I may get something to cover the velcro so I can just use the buckle unless I go in a crowded area.
I wanted a bag that wasn't too techie-looking yet would protect my gear. The 6-million Dollar Crumpler fits the bill just right. It works well for storing my SLR with a couple of lenses, charger, cables, etc. and just as well for transporting gear when I don't need to lug the charger, etc. around.