27 MB + 4.2 MB = 28 MB? Where'd my space go? After getting the "low on space" message on my Nexus One for the umpteenth time, I went to into the "manage applications" screen to uninstall applications I hadn't used recently. I waited for the screen to fully load before I did anything. It said I had 27MB free on my internal phone storage. I then clicked on the "Fooducate" app I had installed. It said it was using roughly 4.2 MB of my internal storage for the application, plus about 12 KB of data. It was installed on the phone and moving it to the SD card was not an option. I clicked "uninstall" and the uninstall process ran. After that, the "manage applications" screen claimed I had 28 MB left. 

What happened to the other 3.2 MB? I would think that if you have 27 MB, and you uninstall a program that's using 4.2 MB of space, you would then have 31.2 MB of free space.

Update:

After turning my phone off and then back on again, and then going to the "manage application" screen, it now says 32 MB free, which is more like what I'd expect. So I guess my revised question is - why wasn't the space immediately available, and is there something I can do to free it without cycling the power?
From what I can make out from your scenario, it seems the culprit is the android's Dalvik Cache.
Quote from a thread in xda forums:-


  When Android starts up, the DalvikVM
  looks thru all of your applications
  (.apk files) and frameworks, and
  builds a tree of dependencies. It uses
  this dependency tree to optimize the
  bytecode for every application and
  stores it in the Dalvik cache. The
  applications are then run using the
  optimized bytecode. This is why when
  you install a new ROM, sometimes it
  takes a very long time to boot for the
  first time. Any time an application
  (or framework library) changes, it's
  reoptimized and the cache is updated.


and it seems that each time you reboot, the dalvik cache reoptimizes.