Even after moving web-based mail to a separate app, I still usually have at least two browsers open at all times - Camino when something doesn't load in Safari, Firefox for tails (a microformats helper), and Safari, which I'm used to, has my bookmarks, and auto-fills forms.
Safari freezes and crashes pretty often for me, but I can't easily switch away from it because it has my history, both in actual saved history and collections of bookmarks which always seem to get dumped into an 'Import' folder when you move between browsers.
Browser history doesn't seem like a lot of data. It seems like a natural choice to keep in a central place, just like the OS X Address Book. However, I don't know of any effort that takes the user's point of view and lets us keep a separate history list, so we don't have to lose data every time we want to try out a new browser.
So - anyone want to step to the plate? Hopefully all it would take is a good API and one browser that works with it - if one WebKit-based browser (OmniWeb) and one Gecko-based browser (Camino) adopted this, it would take something big to make me use Safari again. If a browser imported other browsers' history and made it easy to save & search that history separately, I couldn't think of a reason not to try it out, and see what other features I might like.