I had a similar experience. I forget the exact timing, but it was probably around 2002 - 2003 that Linux felt "good enough." I was at a startup that finally considered putting its "enterprise" stack on Linux.

At my employer in 1999 we were maintaining home-grown binary modification to the Solaris kernel so that TCP segment send and receive were not O(N^2) where N was the number of addresses on the interface :-/ It was, as far as I could tell, an operating system that nobody had ever tried to use before. For anything where we could avoid Sun we used FreeBSD. One of the nice things about the free Unixes of that time was that process and thread creation or destruction were orders of magnitude faster than on Sun. To me, Sun was obviously in a lower category than Linux/FreeBSD/NetBSD.