hm. really weird. I've had some boot problems on an (very) old pc, but none like this.. what about /etc/fstab, have you checked it is correct? I mean, if it's screwed up or something, it might cause problems..though then I think you would get error msgs..but it's a place to look too.. some things (like starting sendmail back in the days) have jammed (and eaten up time a lot) because of they haven't been able to get something done and have just tried and waited..sendmail, for exampe "started" for many minutes in my old distro though the pc wasn't that old.
I'm not saying that mounting filesystems would be the same thing, but if the mounting-process truly is the problem, then there's some major problems getting things done and therefore I'm more than surprised that no errors are shown...
what are you actually mounting? local harddrives only, or is there something else? perhaps the problem could be found by letting some filesystems stay unmounted at bootup, and seeing if it helps.. (that is, to leave those mounts undone that are not vital)