Railhead Design posted some info on the current builds of OS X 10.1:
As far as when OS X will be frozen for golden master, it looks as though Apple will have no problems beating the 5G55 deadline for having everything complete and theres now a very good chance that what Steve will preview on September 7 will, in fact, be the final release version.
The bottom line is this: Apple has been working its butt off to get OS X polished and tweaked to fill the majority of user-requested features. Will it have *everything* we asked for? Of course not, but dont forget that we will receive our first big update after 10.1s release within six months (possibly even in January).
Other users report that the latest OS X DVD Player App now seems to work very well.