I have to start this tip out with a confession: I haven't done a clean install on my main Mac since something like 2004. I mean a true clean install where nothing is imported, I didn't use Apple's cool "Archive and Install" or the newer Migration Assistant, and where every app is installed from scratch.
I had unused preferences in my Library that were dated as last used in 2002. I mean, seriously, 2002? This is a Mac Pro (early 2008). For those keeping score at home, that means it was built in 2008, but I have unused preferences dated 2002? Maybe I should turn in my Certified Geek™ card...
Anyway, I was getting a bunch of runaway processes and finally did a clean install this weekend, but imagine my chagrin when late on Sunday I had two runaway processes on my freshly scrubbed system, Dropbox and osascript. The latter is an AppleScript-related process that was, in this case, owned by Dropbox.
I did some research and found that the problem can be caused if you have multiple instances of the same Mac linked to your Dropbox account. Fortunately, there's a way to fix this, and in my opinion, you should make this part of your regular Mac maintenance.
Here's how you do it: log into Dropbox in a browser and click the triangle next to your account name in the upper right corner of the page, then click on Settings. Once your Settings page comes up, click on the Security tab and look for the My Devices section, as shown in the screenshot below (courtesy of Dave Hamilton).
See how he has a lot of devices attached to Dropbox that are duplicates? Look at all those iMacs listed with office and studio in the name. Those are all the same two devices listed multiple times.
Dropbox Security Settings
(Note that I squished this screenshot up so that it would fit better)
He had seven devices that hadn't talked to Dropbox in two years, and another that was a year old. I had something similar, and if you're a Dropbox user and have reinstalled OS X or Dropbox on your Mac or PC, you do, too.
BTW, if you don't have Dropbox, use my referral link to sign up, and we'll both get 500MB of free space.
To clean it up, you need to Unlink the unused systems by clicking the Unlink button at the far right of that device. Make sure you also Unlink devices you no longer own or use.
When you do so, you'll get something much cleaner, like the screenshot below.
After Dave Unlinked All of His Unused Devices
Once I did this, my problem with runaway Dropbox processes was solved, but there's one more thing I found that you should know about if you ever have problems.
On your Mac, open your Dropbox preferences. You can find them in the Dropbox menu widget by clicking on the little gear and clicking on Preferences. Once there, click on the Accounts tab, as shown in the screenshot below.
Dropbox Mac Preferences
See that button labeled Unlink This Computer? Yes, this is the same Unlink we just did on the Dropbox website, but if you hold the option key down, it turns into a Fix Permissions button. By clicking this button when you're holding the option key, it will fix any file system-related permissions that might have gotten messed up.
Why on Earth this is hidden behind the very dangerous (if you miss-click) Unlink This Computer button is totally beyond me, but it's there, and it's something you should try if you're having problems with Dropbox.