I haven’t seen a place where any “great new features” of v3 are enumerated.

How can I decide which one to start with?

If I learn v2 and switch, will I have to re-learn things?

Does v3 – which has been in beta for like 15 months – crash often these days? Does it have some kind of auto-save so I can’t lose 3 hours work?

Thanks for any assistance.

I’ve been using 3 dev builds on OS X for a year or so as an everyday editor at work, I kept 2 installed just incase but haven’t needed to use it as a back up since. If there does happen to be a breaking change (which is not very often at all) Jon’s pretty quick at pushing a fix out and shutting the update down from triggering ST update checker so others don’t happen to get the bad build.

As a rule for myself I don’t auto update immediately on my work machine and hold off a day while checking the forums for any breaking updates, or update my personal machine with the latest first and decide for myself.

So, IMO, it’s stable for everyday use, just mind the updates and you’re good.

Despite its beta status, for me at least ST3 has been extremely stable since build 3065, on Linux and Windows. I can’t comment on OSX, though there seem to be plenty who are happy enough. Addressing your points:

• I have not encountered a situation where work could be lost that I couldn’t repeat in ST2. The only situation I’ve seen in both editors is editing files over some kind of network connection (samba etc.), the connection going down and my unwittingly closing the editor, with hot_exit enabled and the sublime-project file stored on the remote share. Pretty rare and easily avoidable.
• ST3 is functionally identical to ST2 so there’s no learning curve between the two. The only new things are new features and fixes; when you add these up there are quite a few. If you browse all the posts here you’ll get a fairly extensive list of all the new ST3 features.
• Autosave when Sublime tabs lose focus has inbuilt support with a setting, and autosave plugins are available for timed autosave.

Plus:

• Support for ST2 appears only to be for critical bugs and problems. Small fixes and enhancements to ST behaviour implemented in ST3 have not been backported to ST2.
• ST3 is once again in more rapid development after a short haitus which I hope means plenty more to come.
• If you buy it your license will be valid for both ST2 and ST3
• Virtually all plugins have been migrated to ST3 which was the main reason to continue using ST2 in the past. Those that haven’t are probably unsupported anyway.

In short (and imo): no reasons to use ST2 anymore but plenty to use ST3

ps. original poster, do you hang out at the reaper forums?

Well, it depends on how exactly you “intend to lose” that work. ST does have some mechanisms that can save your work, such as an auto-session save that preserves unsaved changes even between restarts. This is the same for 2 and 3 though. There is more.

Anyway, for me ST3 is superior in any way I can think of.

I have been use ST 3065 for 4 month or more, it is very stable. I have not encounter any crash. I also use ST 2.02 for a long time.
ST3 is faster than ST2 when it start-up, and has same function improvements.
I like ST3, it is very good!