We follow the trunk=current development stream, branch=release(s) approach. On release to the customer we branch the trunk and just keep the trunk rolling forward. You'll need to make a decision on how many releases you're prepared to support. The more you support the more merging you'll be doing on bug fixes. We try and keep our customers on no more than 2 releases behind the trunk. (Eg. Dev = 1.3, supported releases 1.2 and 1.1).
