As I am sure most folks know, the Resco Today plugin (particularly the battery status check) was one of the first culprits claimed for WM5 problems. It appears that they now feel it is resolved with their 5.31 release (December 5). They claim that there is a problem with the function to query battery state. This puts the problem with MS (at least in this case) - rather than Dell.
The thread at the Resco site is at
http://www.resco.net/forums/ShowPost.aspx?PostID=2514
The comment from Juro Janosik is the last in the thread. There are some other interesting comments earlier in the thread about programs performing actions during standby mode that deserve attention as well.
I cannot verify the claim since I fell back to WM2003SE after replacing one x50v.