Dropbox very high CPU usage without any actual data transfer

First run in a terminal:

sudo apt-get install cpulimit && sudo apt-get update

Then use a text editor like gedit or kate and put the following text in the file.

#!/bin/sh
dropbox start -i
cpulimit -e dropbox -l 15

save the file with a name like "cpulimit.sh." After saving go to the icon and right click, somewhere in the permissions section, there will be a box for "make executable" or something similar. Check that box. Go to the autostart program, which you can find by typing "startup" in unity ubuntu or autostart in kubuntu. Add a program, browse, find the .sh file you made and set ok. It should run every time you boot up. In the code above you'll notice there is a '15' that is the cpu useage max. You could probably set it even lower if you want (eg replace '15' with '8' or whatever). I don't know if there is a minimum or not.

My situation might be different from yours, but I was having the exact same problem, however I'm now at a point where my Dropbox is working correctly.

Two things may have been a factor in getting my Dropbox into a working state.

First, specifics of the reinstall. For good measure I started with:

rm -r ~/.dropbox*

Next, I followed the instructions here: http://www.computeractive.co.uk/ca/computeractive-blog/2186872/fixing-dropbox-ubuntu-1204

Basically:

sudo apt-get clean
sudo apt-get update
sudo apt-get --purge remove nautilus-dropbox
sudo apt-get --purge autoremove
sudo apt-get --reinstall install nautilus-dropbox

Second, my situation might be different from yours in that I was trying to set Dropbox up on a secondary HDD since my primary HD is a smaller SSD.

I'd run into problems with Dropbox on secondary drives in the past, so as I was trying to troubleshoot the problem I always had it in the back of my mind that the issue could be related to trying to use a secondary drive.

After having no luck with the solutions you suggested here and others suggested elsewhere, I gave up and decided to see if it would behave more normally if I set my Dropbox up on the primary HDD.

I don't know if it was step 1 or step 2 that did the trick, but after that reinstall with my Dropbox folder on the primary SSH, Dropbox synced and behaved as expected.

Let me know if step 1 solves your problem, because I haven't looked into moving my Dropbox over to my secondary HDD, but I would like to.

Hope this helps!