Just out of curiosity
 

I have read about converting multi-speed moutain bikes over to single speed quite a bit. I was just curious what the advantages are? What about converting from 3 chain rings up front to one and leaving the back cassette intact? Seems like in the case of one chain ring in front and the original cassette in back there would be some serious chain alignment issues. Anyway, I was just curious what people think of this. Thanks!!

1x9 (or whatever) works just fine. Keep the middle chainring and the chainline is no different than with 3 rings. It does help to use an un-ramped ring and some riders feel the need for a guard ring to help keep the chain on.

It is a different experience than a singlespeed though.

I am riding a Single speed bike, with a conversion kit took ak misfitpsycles or something like that :P it's working pretty well, I switched to single speed because of my deraillers problem, I hate those damn things.

DH type chain guide are overkill for general use. A bash ring on the outside and Jumpstop on the inside are the most you really need. I do not even use that much with my 1 x setups.

It seems that shiggy has made it over to here.

You can bend all the teeth off of the big ring and grind it down till its smooth and use that as a bash guard. Thats what a guy i work with recommended and i did it. It works great!!

Ghetto bash guard.......

nothing wrong with ghetto :)

Running 1x9 can give you a much better chainline actually. You can run a shorter spindle (108 instead of 113 in my case), lowering Q factor and allowing a much better chainline while in your 32 or 34. Depending on the terrain where you are, a 32, 34 or 36 would probably be the best options for a 1x9. I run a 2x9 on my race bike, with a 108 BB and 44/30t rings, and love the setup. The Q factor is a lot closer to my road bike that I train on 90% of the time too so it keeps my legs happy, and I find that a 30t is better for a mtb than a 32 for most terrain.
If you rarely use anything but the middle ring, go for 1x9. If you still want a wide gear range, pick up a 11/34 cassette.