MySQL never compiled on Solaris without warnings, and it almost never could pass the full regression test system.
With Drizzle, I felt like if we were going to say we ran on Sparc/Solaris that I wanted to be able to say that we supported it without a bunch of exceptions.
It took us months... and I mean months to get things cleaned up for it. In the process I've gained a bit more respect for the platform (keep in mine... I was a big fan of SunOS, the predecessor to Solaris).
A few nice things I have noticed:
All in all I am becoming a bit happier with the Sun/Solaris environment. I would prefer to just have Debian on the box, with an "apt-get solaris-kernel" to test against. It would give me a better apples to apples comparison. Valgrind and a number of other tools would be nice... but in general?
I am finding that the environment is not as bad as I thought it would be to maintain, and that there are some actual benefits.