I tried. I really did. I made every effort to reuse something existing rather than write my own. But yesterday I caved in when I was told that I was going to have to run my load tests after hours, because the evaluation copy of ANTS Load I was working with doesn't have scheduling capability. It was either start working nights, find something that does have scheduling capability that I can get an eval copy of, or write my own.
The problem with .NET is that it only took me a day to write the basics of a reasonably feature-rich load-testing harness. And I knew it wouldn't take that long, which is what made it so tempting. But of course that same day would probably have gotten me up to speed on some existing tool that a) doesn't have the bugs that mine certainly does, b) I don't have to support, and c) probably has lots more features. It was just tooooooo tempting to write code, rather than download and review some boring tool.
I find it interesting that the CLR made me less productive because it makes me more productive.