It is a mix of new engine features, painstaking BG1 polishing, much improved IWD2/3ed support and hundreds of miscellaneus fixes. Almost a thousand revisions have been made since the previous release, so the following changelog does it no justice:

GemRB v0.8.0:
  New features:
    - iwd2: Chapter 0+1 completable, full spellbook and ECL support
    - multibyte font support (chinese, korean, japanese)
    - favourite weapon/spell tracking, bg1 dreams
    - most gemrb overrides were moved and are now moddable via game override
    - initial bundled gemrb demo stubs

  Improved features:
    - random encounters and spawns (properly difficult)
    - iwd2 combat, stats, spells, skills, effects and actions
    - animations, speech, input
    - looting, worldmap, hotkeys (work everywhere), fatigue
    - bugfixes

Gamewise, BG2 and IWD1 haven't received many changes, but for the first time IWD:ToTLM is playable to the end. IWD2 made the biggest strides and its Prologue can be played through with some minor caveats. BG1 got polished to make the whole TotSC a pleasant and complete(able) experience, something we thought we had already achieved. It turned out nobody tried Durlag's tower or told us of all its problems before. PST support had no major updates, but a playtesting attempt revealed most of the todos and that the plot can be followed far into the game.
The last two things would not be possible without extensive, reactive and documented testing by "traveler" and "chiv" respectively, which is greatly appreciated. This allowed the thralls to focus on actually fixing those problems and cursing at the idiosyncrasies of the original implementations. While PST hasn't seen many changes, we now have a detailed list of gameplay issues to work on and test with. Interestingly, IWD2 support turned out to be much more complete than we had anticipated, so the doors are wide open to making it as nicely supported as BG2 in a release or two! We've also started a small dataset that is bundled with GemRB, a sort of demo. On that note, we're looking for help in any available form!

To make collaboration even easier, we moved our GIT code hosting to Github. Existing users of git gemrb don't need to restart the download, but just run "git remote set-url origin git://github.com/gemrb/gemrb.git" first and then continue updating as usual.