- The write/build/test compile cycle is slow as f-ck
- C# isn't really all that supported outside of Windows, which sucks for server centric apps. Yeah, you can use mono, but why?
- C# is grossly verbose in contrast to ruby/php/python
- PHP is instant gratification. Change, reload browser, lather, rinse, repeat.
- Lack of open source libraries + libraries you have to pay for = suckage
Really, though, C# and .NET are the frontier of lowest common denominator developers. The kind of dudes that wear teva sandals with socks and tucked in short sleeve shirts. You can also call them copy and paste developers, because that's essentially what they are. Most of the innovation in the last 5 years has come from the open source camp, not the corporate drone MS army.
I used to be a .NET developer, btw. Wouldn't touch that shit with a 10 foot pole these days. Not a chance in hell.