I am the systems administrator at a 400 employee software company. We have possibly a maximum of 20 mac users mostly in the Art Department (Mac Desktops), a few in senior management type positions and a few software developers. Our help desk does not have the knowledge to support macs, so I have become the unofficial support person for it. I don't hear about to many issues and when I do, it usually turns out to be an application issue (can't make program xyz do this, can't make program zyx do that (mostly because they are not meant to)). For the most part our mac users are pretty self sufficient. Combine that with the fact that Macs generally don't have the same issues as a regular PC means I don't get bothered too much to help.
Although I have a company supplied workstation (a big monster HP desktop), I still bring my personal MBP into work and do most of my work on it. It has all the advantages of being able to run great Open Source software that I need to work with (we are primarily a linux shop, and use MS/Mac on desktops, except for us SA's who all use linux workstations), and I still can use commercial software for specific needs (ie Open Office (open source) for my office suite and MS Entourage (commercial software) for my mail/exchange server needs). While I can use company funds to purchase personal software for my MBP, I find that I usually use an open source equivelant if there is one thereby saving the company some money and in the proccess, making the TCO on the macs lower in the end than for PC's
Sorry for the longish post!
Cheers