I use Tippex (yes it's just a brand name for a correction fluid) all the time. It's not a complete replacement for ordinary filler but it it very useful.
Places were it's really useful is small gaps were you don't want to sand, just apply let it dry (very quick) then with a Q-tip (brands! there we go again) dipped in alcohol remove the excess then it's ready to paint, you might have to do a second application to completely hide the gap but it all takes only a few minutes.
You can sand Tippex, but because it's softer than normal filler it cloggs wet 'n' dry paper very quickly so you need plenty of water to stop it chipping.
For anything larger I use Milliput because it doesn't shrink.