When I was making the Halloween cupcakes a couple of weeks ago, I wanted to pipe on the green stems for the pumpkins and the faces on both styles. But I didn't want to wash the piping bag in between, because it's a bloody pain in the arse. Plus, I wasn't sure I'd have a small enough tip to do the faces well. So I went with the lazy option - zip lock bags.
You really can't use them for any kind of precision decorating work (not that my decorating is even remotely precise!), but it sure saves a lot of washing up. Especially when you're working with a crapload of black food colouring...
Mmmm, delicious... Doesn't look at ALL like something off the set of Supernatural!
So if you're in a rush or need a teeny tiny piping tip that you don't actually own, go with the zip lock bag. It's cheap, it's easy, and it saves a hell of a lot of washing up! Plus, it can have pretty decent results with a little bit of practice: