I am thinking of reading up and running a game of M&M.  It looks like 2e has more stuff published for it than 3E does.  So that begs the question, what are the differences between 2E and 3E?  Is it possible to use 2E stuff in 3E without much work?  What about vice versa?

Thanks in advance! :)

There are a lot of similarities in the core mechanics, but 3e changes quite a lot about the inner workings of the system.  The way it handles affliction-type powers and "status conditions" got formalized and standardized, as well as how "degrees of failure" work on saving throws, with the staged failure mechanic being baked into the core system.

The game also uses a much more comprehensive and expansive version of the Time and Progression table that lets you translate power ranks for all kinds of things (like Strength to carrying weight, and carrying weight to throwing distance, etc...)

3e is capable of almost everything 2e is capable of, but it's very much condensed into the core mechanics.  Most of 2e's published supplements are just colorings and flavorings of Ultimate Power, with a smattering of genre-specific content, and a few gentle massages of the system.  It takes a little work to extract everything back out, but it definitely can be done.  (And where it can't, it's probably on purpose.)

Translating stuff from edition to edition is deceptively simple, but requires pretty careful vigilance to avoid things like getting a "better" or "worse" version of a power than could be built using the other game's existing mechanics.  It's a nonzero effort to check your work, despite things looking very similar.

Cool, thank you for your reply.  It does sound like it would be worthwhile to do in order to get the stuff I want into the edition I have.:)