reiserfs used to be a serious contender at one time...

but I stopped using it after a couple of problems I blamed on my ignorance and didn't bother investigating. Looks like those may not have been my fault :-)

...from http://hardware.slashdot.org/comments.pl?sid=538036&cid=23241212 :

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ReiserFS isn't even a has-been file system, it's an almost-was, and was never a real contender for a top filesystem, no matter how much some users loved it.

Why wasn't it taken seriously by everyone?
- When it encountered problems, it crashed spectacularly. You didn't just lose a file or a block of a file, you lost entire trees and could get metadata instead of file data and vice versa.
- It lacked basic tools, like "dump"/"restore" or "freeze".
- The fsck rebuild process was a security nightmare. A user could craft a file with data that would appear to the fsck process to be metadata, and take over the system after a reboot. In typical arrogance, the solution was "don't reboot, then".
- It didn't support streams or compatible metadata, thus no Mac sharing or SELinux. SELinux in particular is a requirement for many big corporations right now, and not supporting it means no buy.

And, yes, the arrogance of the maintainer played a part too. But even with a much nicer guy running the show, it would not have been a serious contender for the throne.