Possible answers:
1. There is, or not too long ago used to be, a bug in rapidshare resulting in sometimes unreasonably high download counts for a single file
2. Somebody is reposting your links elsewhere - not at all uncommon
3. You post really good stuff that has a lot of fans.
An overnight jump of 2800 downloads, could be due to a bug... but it's not impossible. However, over time one file can get way over 2800 downloads.