I've upgraded to 4.1 and this is still happening, strange though it may be, it is definitely dependent on other apps. This is why it has taken me so long to trace the cause. I do not know if this is down to them using memory or processor, but would imagine memory.

I'm seeing it increasing by small numbers of k on my development machine by opening Word, closing it, opening Excel, closing it, etc. Out on the customer's machine it is being run on a terminal server and they are seeing jumps of 5Mb up until the machine runs out of memory and falls-over.

example from my machine:
TIME MEM USED
11:18am 14972
11:19am 14976
11:20am 14992
11:21am 15020
11:22am 15040
11:23am 15052
Stopped Doing Anything Else On The Machine
11:23am 15052
11:24am 15052
11:25am 15052
11:26am 15052
11:27am 15052
11:28am 15052
11:29am 15052
11:30am 15052
11:31am 15052
11:32am 15052
Screensaver Kicked In
11:32am 15056
11:33am 15056
11:34am 15056

If you have a database with a large table including blob, number & varchar columns it should be a 5 minute job to replicate.

Should you still not be able to replicate it let me know and I'll try to find the time to write some SQL to create a large table and populate it, then modify my timer app to use it instead.