I think Dotfuscator Community Edition shipped with Visual Studio is quite a naive solution. It provides only symbol renaming and does not obfuscate control flow at all. And if someone decides to stole your code it will only need to refactor back all names, which is quite easy with small amount of classes.
Also you can rely on not so perfect decompilation provided by Reflector (it usually messes switch blocks, makes lots of gotos, mismatch if-else blocks, etc.).
But I suggest you try Eziriz .NET Reactor. It costs only $179 (AFAIK best price/features ratio). It provides standard obfuscation techniques such as symbol renaming, string encryption, control flow obfuscation. As a good bonus it creates native launcher for you app, which will contain your main assembly and all third party references encrypted and loaded on demand. Plus it provides some licensing capabilities.
Anyway reversing .NET application is not so hard, I did it for fun and can say that it's only matter of time and money (and of course common sense) how fast your application will be cracked or reversed.
