froyok, 
Dropbox has a "fun" bug since a few weeks on my machine.
Each time I wake it up from sleep, and a file is modified, Dropbox app becomes crazy and eat up all my ram.
Take 5 minutes for the system to notice and kill it (or maybe it crashes because it can't allocate further).
I doubt I will bother report the issue, given how unhelpful their support is on their forums.