I'd think the problem with bumping the version number if you're remaining compatible is that it signals to the end-user that you're not compatible. i.e. when I

I'd think the problem with bumping the version number if you're remaining compatible is that it signals to the end-user that you're not compatible. i.e. when I start using 2.x the constraints I'll put in my list of libraries is < 3.0 (because otherwise my project could randomly break upon 3.0's release, depending on whether it's compatible or not).