Is e4defrag ready for use?
Solution 1:
According to one of its developers, Akira Fujita, e4defrag needs more feedback - which IMO translates to "not ready for prime time". I wouldn't use any defragmentation tool that's not thoroughly tested.
Here are some interesting slides from his recent talk at the LinuxCon 2010.
e4defrag is now in the development version of Ubuntu 12.04, see its man page for details.