if you leave the cages out, you'll probably have to add a bearing or two, but for the BB i'd use them. there's nothing worse than losing one down the chainstay or up the downtube and then having to open 'er up again and get it out when it starts rattling. not to mention how awkward it can be just getting them in there in the first place.

i've found cartridge bearing BB's to be a godsend, on the whole.