This tells me that I have only 492MB free on my computer. It sounds like a lot, and it is, but these days we're so greedy with disk space that it won't last long if I don't watch it carefully.
Yet I am seeing only 1.4GB total space, and I expect 4GB?
Some Eee Silliness
Something that is confusing about this picture is that the little Asus Eee that I am using is doing something a bit silly with its file systems. In order to be able to restore the original software on boot, the Eee keeps a read-only copy of all the software distributed with the system. This is typical in the PDA world of Palm, but not very usual with a computer system. With a computer like the Eee, there's really no need for this, as the computer can be restored from a USB device. I have found a way to remove this business and recover that disk space, but I haven't tried it yet.
Using du
The du command (which stands for "disk usage") will show you how much space is used in each subdirectory. Here's my accumulation of mail messages on my Eee. (Frightening—110MB after only a few months!)
~/Mail $ du -h
16K ./friends
68M ./rmiug
4.0K ./drafts
2.7M ./CLUE
12K ./returned
24K ./cygwin
188K ./science
368K ./school
600K ./oracle
1.4M ./other
11M ./opera
9.3M ./mingw
3.0M ./spam
2.1M ./archive/mail
2.1M ./archive
12M ./junk
16K ./me
110M .