After upgrading to Ubuntu 11.10, I noticed some serious issues compiling and building GNU Radio. I spent the weekend working these out, and I'm happy to report that as of Sunday night, the git maint/master/next branches can all be built on Ubuntu 11.10 (and all previous builds, too, of course).
The work isn't quite done, yet, I'm afraid. There are still some bootstrap issues as the autotools guys have becomes a bit more restrictive/careful. The warnings that are generated are annoying but appear harmless. I worked out what I could, but there's one or two more that are alluding me right now. I'd appreciate any assistance in tracking this down that anyone wants to give me.
The other error was that we didn't explicitly link against the Boost filesystem library in a couple of places. That was another easy one to fix.
But the big issue came because of Ubuntu's change to using Qwt 6. We had been using version 5.2 since we build gr-qtgui. The change to the new API was not trivial, especially when trying to maintain backwards compatibility with 5.2. I'm happy to say that this has been achieved. The code's a lot uglier because of the Qwt version checks, and while I could have probably done it a bit more cleanly, this is still the right way to do things.
While the update to Qwt 6 was pretty painful, the new API and changes that they made have created a much better system. In particular, the waterfall plot has been greatly simplified from version 5.2. Once version 6 starts to take hold in all of our other OSes, I'll go through and clean out the old stuff required in 5.2. This probably won't be for a few years, though, but it will be nice when we can move on and create more simplified implementation.