Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8F190 Safari/6533.18.5)
I've managed OSX server 10.3 - 10.6 & will be using 10.7 when new servers arrive.
I've also managed windows 2003 & 2008 servers, small business & enterprise 32bit & 64bit. Virtualised & non virtualised (on dell & hp hardware).
All have had issues. None with 100% uptime over a year.
But no show stoppers & not enough for me to really recommend one above the other.
However, OSX server is very very flexible for the cost compared to win server.
But the support is poor. (well is in the Uk).
So for enterprise I'd suggest win over mac server for business critical stuff.
If you've a small company (50 users) osc server is a real bargain depending on what you use. (iCal, wiki, cross-platform native filesharing, ldap, mysql, web, VPN etc...) $49?????!!!!!! woah!!