Likely, you have noticed there were no nightly builds on the previous week. Now the issue is fixed, and they're back again. Moreover, v4.1 installer is updated to the today's nightly build - I assure you it is very stable (~ 6-7 tests are failing there dependently on configuration - that's normal, they show tests for works in progress and few known issues).
If you have some time, please download and install the latest build: your feedback would significantly help us to deliver stable v4.1 release on the end of this week. As you know, installer was one of the most disappointing parts we had so far, and I hope the current one won't suffer from any problems of its predecessors. Please compare your own installation results with expected ones.
I know what I suggest is quite similar to "help yourselves" ;) But... I feel there is no other good way to do this. We have a limited set of configurations, and although everything works locally, I still get reports & fix some pretty strange issues there. E.g. few days ago one of DO4 users helped us to identify a serious bug preventing DO4 from installing on 32-bit Vista. I can't imagine why there was "HKLM\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\9.0" subkey on 32-bit Windows, but it is the reason of the problem. And I suspect this isn't a very unique case - similar issue was described at our support forum earlier, but that time we were unable to identify the bug. So testing installer for complex framework is complex. But I hope we'll accomplish this - at least by this way ;)