ASP.NET Temporary files cleanup
Yes, it's safe to delete these, although it may force a dynamic recompilation of any .NET applications you run on the server.
For background, see the Understanding ASP.NET dynamic compilation article on MSDN.
Just an update on more current OS's (Vista, Win7, etc.) - the temp file path has changed may be different based on several variables. The items below are not definitive, however, they are a few I have encountered:
"temp" environment variable setting - then it would be:
%temp%\Temporary ASP.NET Files
Permissions and what application/process (VS, IIS, IIS Express) is running the .Net compiler. Accessing the C:\WINDOWS\Microsoft.NET\Framework folders requires elevated permissions and if you are not developing under an account with sufficient permissions then this folder might be used:
c:\Users\[youruserid]\AppData\Local\Temp\Temporary ASP.NET Files
There are also cases where the temp folder can be set via config for a machine or site specific using this:
<compilation tempDirectory="d:\MyTempPlace" />
I even have a funky setup at work where we don't run Admin by default, plus the IT guys have login scripts that set %temp% and I get temp files in 3 different locations depending on what is compiling things! And I'm still not certain about how these paths get picked....sigh.
Still, dthrasher is correct, you can just delete these and VS and IIS will just recompile them as needed.