Our IT setup is Linux for everyone who is developer or QA (15 Dell Ubuntu machines) and Mac OS X for everyone else (20 people). We also have 2 windows QA machines.

We might not be "Enterprise" yet but it works well for us.

Macs may seem more expensive up front but the cost of buying the machine is not its whole cost. Total cost of ownership is important. Downtime for highly paid employees is just as bad if its their desktop as if it is a server.

Mac's have fewer problems and have fewer downtime. Over 3 years we've never had a Mac desktop go down. I can't imagine a similar statement coming from a similar sized business running Windows.