If you read this thread carefully you will see other examples of people who have had their N900s fixed; sometimes it took them more than one try, so you aren't alone.

In one of those messages you must have missed they say that sometimes the N900 gets sent to third-party repair people who don't understand this is a known issue.

I haven't read this thread very carefully myself, because I don't have this problem. I was worried about it for awhile, but it seems fine on my N900. Also, since I don't usually charge batteries on the phone, but in a separate charger, I don't use the USB connection that often.