[fbuilesv]

I think I read this advice on Getting Real (http://gettingreal.37signals.com) and it's been useful so far: listen to your customers and their requests but don't do anything about it. Important stuff will keep coming back frequently so by the time you get the 10th email asking for custom emails you can start considering to add it as a feature.

Caveat: This works as long as you many small customers. If you have a few large customers you can go for the customization route and just charge them a lot to make it worth the extra effort.