Comment 148 for bug 131094

Things I can reasonably confirm are not the cause:
-Hardware drivers (I've had this problem across several different machines)
-Versions of Ubuntu (I've been having this bug at least since Hardy and I believe before that)
-Different distros (I found a forum thread where people were having the same issue on Fedora)
-Dist-upgrade (I always install fresh)
-Search Indexing (Problem occurs even with indexing completely disabled...if there is an issue, it's a symptom and not a cause)
-Firefox versions (Fsync bug was fixed a long time ago, and people have tried reverting to Firefox 2 without success)
-Filesystem in use (People have reported the problem on ReiserFS as well as ext3)

Reasons I think it's the scheduler:
-It was reported switching schedulers helped this problem on Fedora which also uses CFQ.
-I've tried both deadline and anticipatory schedulers and then copied large numbers of files and the system was 95% more responsive.
-People first started reporting this problem on the Ubuntu forums around the time CFQ was switched to the default scheduler, which I believe was around the Edgy/Feisty timeframe.
-People have reported the problem doesn't exist on the 'server' version of Ubuntu, which uses the deadline scheduler instead of CFQ.

There may be other issues at work that cause similar unresponsiveness, but I think the scheduler thing is it for most people.