Off and on but never given it up.
I've been an Apple partisan since 1994. I graduated from high school in '93, but my high-school was still using PETs and C64s. My first exposure to what I consider a modern PC was that fall when I started at the local community college and taking basic computer labs. These labs covered the ins and outs of Microsoft Windows 3.1 and Office.
I loved it. It made immediate sense to me. Then, a few weeks later, I was in the college library, and I found this tiny room in the back - almost a closet - that had four computers in it. Three of them were Macintoshes. Two IIfx's (yeah, really) and a Quadra 700. All running System 7. Something about those little machines seriously appealed to me. I found myself migrating back to that room all that semester. Eventually I met up with the other mac-users who told me that there were more macs on campus in the Art Department.
Next semester I took Art. I can't draw to save my life, but I took art. I also used a student discount to buy my own mac at the beginning of that semester: A blazing fast PowerMac 6100/60. I was cutting edge. Hard core. I played countless hours of Marathon on that machine (yes, I knew Bungie back when they only made games for Macintosh).
I ended up befriending the art teacher and also discovering the intricacies of the Macintosh operating system. The school had a few hundred PCs and about 30 macs (aside from the 3 in the library there were six in the art dept. and a couple dozen on the desks of the college staff). The PCs guys didn't want to deign to troubleshoot macs, so I ended up working part-time for the school doing mac support.
I was in heaven. Mac support is 1% hardware issues like foot-snagged, unplugged cables or third party drivers and 99% user support. Basically somebody would need help figuring out how to do something and my job was to figure it out and show them how.
This went on for a few years, and eventually I switched colleges and also bought my first laptop: A PowerBook 1400
Around 1998, though, I was starting to fall out of love with the Mac OS 9. I'd bought the BeOS betas and had toyed with some of the ever-maturing Linux distros for PowerPC. The only thing thing that the Mac had going for it was superior processors (PowerPC) and the professional software I was rapidly becoming reliant on (mostly Macromedia and Adobe titles).
Then Apple announced their acquisition of NeXT and I decided that NeXTSTEP looked worth waiting for.
I loved OS X from the start. I started running OS X full-time, on all my machines at version 10.0.2 and never looked back (by this time I had acquired a G4 Cube to add to the menagerie).
I had another dilemma a few years later, though, when I wanted to start gaming more. I'd been buying what mac-titles were available but it was impossible not to look with envy at the Windows world where games were released sometimes for years before they got ported to mac, if at all. But productivity, reliability and longevity were too important, and the release of EQ for mac sealed the deal. In it I had a never-ending game and it was on my OS of choice.
I have still caved from time to time to the itch to try something new and have put various Linux distros on my PowerBook G4 and the old Dell I have in the front room (it usually runs Win2000 so my boy can run his Star Trek Next Generation Interactive Technical Manual). But I always end up coming back to OS X because I like things to just work and I find OS X far, far more intuitive than any version of Windows I've encountered - and I've encountered them all.
Now, I'm on the edge of buying my first Intel Mac Pro and retiring my G5 workstation to it's new position as NAS for my house. At that point I'll actually buy a copy of Windows to install on boot camp in case I come across a game that I just have to play. Since I now mostly play Blizzard and iPhone games, though, that's probably going to be pretty rare, indeed.