I got billed because when Azure went from CTP to RTM, they started charging customers, no surprise there! but because I forgot I had some demo services deployed in Windows Azure, I got charged. So I quickly deleted them.
I started using Windows Azure compute again - historically I've only used Windows Azure AppFabric which in most cases doesn't use Windows Azure Compute - i.e. you don't normally host any custom services in Windows Azure, instead you use the service bus to relay messages back to your on-premise data centre.
It's good to know now that Microsoft make this very clear in the new-ish management portal (written in Silverlight):
So now it is fairly explicit, so no excuses people, when you get billed for deployed disabled services, don't complain! To stop billing from occurring, you need to delete the services using the management portal entirely, that is of course you don't intend to use those services.
Heads up on the new portal, I like it, it's a much improved user experience over the old multi-site portal for each SQL Azure, Windows Azure and Windows Azure AppFabric. Now management it done under one portal site.