For me it was with C64/Spectrum/MSX.

And I was at the Spectrum side at first, but switched to C64 when I realized it was superior.

Ummm I'd have to say I got big on fan-bias last round, Before the X-box it was Playstation or Nintendo, but I coulden't really base a bias off that, it was like comparing Fish to Cow, they both offered protien just whichever happened to taste better was all preference. I kind of changed my view on video games and got really into Surealistic, Epic cinematic type games (started with Chrono trigger then moved to FF7, Metal Gear Solid, Chrono Cross, Etc.) So going with Sony was a no brainer for me. That and the fact that at the time Sony offered things like multi-use hardware, backwards compatiblilty, and a crapload of RPG's which I'm really big on.

But then Microsoft -_-;;; First off let me state that I HATE Microsoft. I've dealt with there buggy software for sooo many years >< But but but! I have no real gripes with the first X-box, looking back at it in retrospect it introduced  a new concept to console gaming (Hard drive) and it was a fairly solid system, I hated the controller but that was about it, I just couldent buy it because it was MS.

And then the 360, they busted, a friggin MS on they're own console...  They put out a very strong first product, got the fanbase hook, then BAM they release a HORRIDLY unreliable piece of hardware, one SKU of which didnt even include what EVERY owner of the first gen loved about it in the first place! 33 percent failure rate was WAY to high for ANY HARDWARE manufacturer, and I would have understood if it was like, a reader, or a battery in a controller, but it was the friggin processer/graphics card ><. Then rumors of the "disk eating" which sad to say, are definately not rumors ;-; (My roomates lost 3 to the beast ), then consoles bricking durring a RROD durring an update, etc etc etc. I couldn't believe that MS did this to the world AGAIN. 

So as far as playing games go, I'll play games on the 360, I just wont buy them, and its only been a few so far that I just had to play (Bioshock is pretty 1337 :P )  

ANYWAYS back to the point at hand, I noticed a fan-boy war last gen with the introduction of the Xbox. 

 That is because you are not looking. Because you don't want to look.

Seriously, saying what you just said, at this moment in time is just... I don't want to call it fanboyism, but you just see what you want to see and nothing else.

I first noticed it in the Super NES / Genesis era, like others said. The thing is, without the internet, people had to talk and get along in real life...I don't know about you guys, but I don't see such heated, "I hate console X" debates in real life...people want to get along. On the Internet, nobody cares about getting along so they can say whatever they want.

Had the Internet been available, I'm sure fanboy rantings would have been just as bad back in the 16-bit era as they are now. I remember after Mortal Kombat came out, magazines started getting flooded with "envelope" art of Mario and Sonic performing gory fatalities on each other. It's pretty funny in retrospect.

 There was some in the Genesis vs. SNES but it wasn't as rabid as the Playstation Vs. Dreamcast... That one was the first one, in my opinion, that seemed to have people so galvanized that they would support one or the other to the death.  Clearly this generation takes the cake, though, because of the ease of access to the internet...