37Signals gives a ton of good advice when it comes to running a web service, and some not so good advice.
Here a gem 37Signals provided:
Ask 37signals: How do you process credit cards? http://www.37signals.com/svn/posts/753-ask-37signals-how-do-...
It was so good, that the CEO of Braintree Payment Solutions referenced it when talking about the same subject:
http://www.braintreepaymentsolutions.com/blog/annual-credit-...
Now that it's tough to raise money, "copying" 37 Signals and charging for your products on a monthly recurring basis is spot on for most new web services. I don't listen to everything they say, but every now and then they have it figured out.