I've a couple of questions regards PS3's BRD playback. The first is how do you stop watching so you can resume from the same place? Watching Spiderman 2, whether I stop, pause, or anything, it always starts playback from the beginning.
Some discs have their own bookmark feature which needs to be used when present. It seems to usually be in the chapters menu, so check there for info on setting a bookmark. I believe it generally uses the colored buttons on the remote.
I think discs that don't support bookmarks will resume automatically but not sure if that's 100% true. At least some should. It is really unfortunate the resume isn't consistent across discs.