A warning for people using the *static binary* version of Bitcoin on a Linux/UNIX-ish system (tl;dr: **Berkely DB databases are not forward compatible**).
The static binary version of Bitcoin is linked against libdb4.8 (see also [this Debian issue](http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=621425)).
Now the nasty thing is that databases from 5.X are not compatible with 4.X.
If the globally installed development package of Berkely DB installed on your system is 5.X, any source you build yourself will be linked against that. The first time you run with a 5.X version the database will be upgraded, and 4.X cannot open the new format. This means that you cannot go back to the old statically linked version without significant hassle!
### Ubuntu 11.10 Warning
Ubuntu 11.10 has a package called 'qt-at-spi' installed by default. At the time of writing, having that package installed causes bitcoin-qt to crash intermittently. The issue has been reported as [launchpad bug 857790](https://bugs.launchpad.net/ubuntu/+source/qt-at-spi/+bug/857790), but
isn't yet fixed.
Until the bug is fixed, you can remove the qt-at-spi package to work around the problem, though this will presumably disable screen reader functionality for Qt apps: