I know this has been commented on in various places, and I think I've read most of the relevant threads. I recently had a situation where I did the following:
Search for a file ('invoice.pdf') in Everything, using "invoice .pdf" as the search string.
Copied it (from the Everything window) to a new location (copy, not move) which happened to be in Dropbox.
Renamed it to 'Jul 2011 invoice.pdf'
Downloaded 2 others from a website directly to the dropbox folder and named them 'Jun 2011 invoice.pdf' and 'May 2011 invoice.pdf'
Everything window now only contained the original 'invoice.pdf' and the 2 direct downloads, but not the one which was copied and renamed locally.
Perhaps there was some kind of race condition between the local copy operation, the renaming operation and the dropbox sync. Anyway, I've added Dropbox as an 'included' folder as per the various threads, and this regenerated the db, so now all 4 matching files appear in the list. But I'm not convinced that adding Dropbox as an included folder really solves the problem - isn't the fact that it regenerates the db just a short-term solution?
How about a 'regenerate' button in the Everything interface, just to make that process easier, until the exact cause of the bug is identified?
Happy to do more testing if there's anything specific needed...
Cheers,
Dave.