Interesting. How many files do you have? I recorded a trace of dropbox executing on my windows machine (mostly flat folder hierarchy, ~500MiB , ~1000 files) and the file I/O for querying all my data took 71542.070μs (0.07s). I believe dropbox also does some extra things (reading the NTFS journal, its own file cache-journal, updating hashes, etc ) and so the total File I/O cost was around 2944815.431μs (2.9s). Note that the I/O happened sporadically, and the wall clock time is higher as expected (it didn't block the scheduler from scheduling other processes).

I assume since my data was synced and didn't need to be indexed all over again - I got some savings there. Maybe your dropbox configuration data is corrupted and thats why it needs to index it all again.