I hate autosave (and the auto-quit/auto-resume feature) with a passion. It can cause dataloss in the (for me) very common scenario of loading a file, editing it, then doing "Save As" to another filename. That "feature" alone is enough for me not to ever switch to Lion or later voluntarily.
Then there's the new defaults like inverse scrolling (I suppose it works for a touchpad or touchscreen, but I find it completely counterintuitive for a mousewheel), conversation view in Mail.app, autohiding scrollbars, half-baked full-screen "support" which is useless on multi-monitor setups, auto-correct, more restrictive sandboxing breaking apps, a dumb app-store rather than being able to install software the way I chose. I know I can disable those things or just ignore them, but why bother? Paying to switch to another version of an OS, which takes time to install, where I need to fix the settings to something sensible, yet gives me no benefits? No thanks. There is quite literally not a single change that is useful to me or an improvement to my workflow. Mountain Lion and Mavericks get rid of even more things that I use and do not offer any improvements I find compelling. It may work for some users, but it's not for me. Heck, I'd rather switch to Windows Vista or even Windows ME!