When does swap decreases

[Francisco Reyes]

My swap used to be 30MB+
I increased from 256MB to 384MB.
For several days swap usage was zero. Then I saw it increase to a few 
hundred Kbs.. and now it's up to 10MB.

I am wondering if it's because swap is not going down or there is now that 
many more programs running (which I doubt).

Before the memory upgrade the swap was very steady at 30MB so after a 
128MB memory increase I am a little surprised my swap seems to be staying 
around 10MB