On my two machines one with Ubuntu 12, the disk usage analyzer is very slow, really hangs in showing usage. For example I have had the analyzer open for an hour, and it still does not show usage. The other folder sizes take some time to show.
The laptop is a HP Pavilion laptop dv6, the other is a custom machine which is a few years old. Other programs are not slow. Both machines are showing low disk space errors, but even prior to these messages showing they were showing that.