From what I can see you can forget it. 1.0 is what is being pushed and in 1 day (from what I can tell since I was able to access the mygwt site yesterday) my basis for info and solutions on 0.5 has disappeared. In another post Darrell said that it's not feasible to port the data over the Ext which I agree would be a large job but I cannot see why a readonly archive cannot be made available for the previous version. Also I believe I read in another post that SVN source is now only available to commercial customers thus I would presume that even incrementally bug fixed/updated versions of 0.5 (if they were to exist) would not be accessible to Joe public.
I will move over to 1.0 as soon as I can but I'm on a deadline to get a demo up and running and I don't have time to go messing around with a new lib, at least not until after the 17th of May (despite the low probability of it breaking my current code but again I just don't have time right now to investigate).
Of course the above is speculation merely from what I've observed between yesterday and today.