What's the best way to defrost ice-cream/sorbet quickly? I made some sorbet at the weekend, and realised just when we were due to serve that I had forgot to take it out of the freezer to soften, and so it was rock hard.

What is the best way to bring it to a usable temperature quickly?  We chucked it in the microwave and then hacked it with a spatula, but ended up with a lumpy texture as many parts were still very frozen.  Any ideas to avoid a repeat in the future would be appreciated.
Don't.  Ice cream is hard.  It melts slowly.  Instead, focus on scooping.  

Get the largest spoon you have, or ideally, an ice cream scoop.  Fill up a cup with boiling water, or as hot as your faucet will get it.  Dip spoon/scoop in the water.  Scoop.  Dip.  Scoop.  Shake off excess water as you go.

Like a hot spoon through ice cream.