This seems like something that should have been a given, since all pc-based web browsers have this feature. Even my blackberry allows for the use of folders to organize bookmarks with the default web browser and Opera mini (and I think maybe Bolt also, but I don't really use that browser very much).
If the Android people are listening, PLEASE ADD THIS BASIC FEATURE.
I just bought an Android based phone, and I can't imagine how cluttered things will be without the ability to categorize bookmarks.