Yet again I've been taken aback by just how cool C# is. Up until now I've felt limited by the tools I've used (Actionscript, PHP, etc) but now I just feel like what I can do is limited by my knowledge, and that when I read the right articles I will be able to do anything in C#.
The .NET namespaces are also fantastic - the functionality available is huge. I'm just learning how to inherit some of the default interfaces and classes into my own work so that I can do incredible things with hardly any code.
Today's trick? Bind a custom object to a server control. Lovely.