Bikes: Anybody ride a single-speed or fixie?

I'm considering converting my current mountain bike to a single-speed and could use a little feedback.

I don't really recall seeing other full-suspension singlespeeds; is this a really uncommon thing to do? I'm riding a 5 year old K2 that I love to death, but it's seen better days. I've put a couple thousand hard miles on her and while the frame is in great shape both the front and rear shocks leak oil and I'm in need of some new wheels. Luckily it doesn't have disc brakes so a single-speed rear wheel shouldn't be too hard to come by. All I'd need is a new wheel, sprocket, spacers, and a chain tensioner, right?

It'll mostly be used for commuting and riding around town but I'd still love to cruise singletrack with it. Any ideas on a good gear ratio?

I'm also looking into buying a cheap fixed gear bike. No brakes, 1 gear, no coasting, chrome-moly steel road frame. I rode one a few weeks ago and despite being pretty nervous on it I loved the sensation. Not having the ability to coast or stop suddenly really forces you to become more aware of what's going on around you. If I picked up a fixie it'd be for city riding and some racing at a great velodrome here in Portland.

Here's the K2 that'd undergo the mutation:

I finally decided on a frame:
sheldonbrown.com/harris/sur…

Once I get some wheels picked out I'm going to order it and put the rest together. Yes, I'm going to have a front brake. :)

The one question I have left is: toe clips or clipless? I've biked for many many years on clipless pedals now, and aside from the hassle of having to wear shoes with cleats I don't see a reason to go back to toe clips. If I do go clipless should I stay with SPD-compatable ones, or go for something a little more slick like Speedplay Zeros?

First off, frames made for single and fixed are NOT spaced differently. They're all 130mm. What's different are the hubs. Second, use clipless on a fixie. You need the push and pull. I wear SPD on my fixie because that what I happened to have. Most of my friends swear by Speedplay or Crank Bro. I never road my fixie with a brake, I just forced myself to learn how to control my speed which did take a little while, but well worth it. Learn to stop skid, it's super easy and def manditory.