I've grown to appreciate both SS and fixed riding. I had a whole separate draft reply started the other day on this thread but it kind of started going off the rails and deleted probably for the best. I first tried a dedicated SS build on an old curbside rescue road bike after a couple longer/hillier local rides where I just didn't shift and realized those were some of my most enjoyable rides to date (~10yrs ago at the time.) That rescued road bike was only my second bike and first actual road bike, complementing my old rigid 26" MTB. I put enough work into it to get it rolling with the original 2x6 (stock 52-40 x 14-28) drivetrain and downtube shifters and enjoyed the luxury of bar/stem swapping with no shifters or excess cabling to address. Those memorable no-shift, rolling, road rides I think I stayed in the 40x17 or 40x15, so when I later settled on a rebuild plan and drivetrain update for what was meant to remain a geared road bike I also took the opportunity to acquire a true SS rear wheel to ride while obtaining the rest of the build parts and/or cleaning/servicing whatever I'd reuse for the geared build. There's a lot more to the story on this particular build, it's ultimate demise, and my personal evolution into DIY bike tinkering, finding my way here and to iBob, etc. which I will spare at this time, but that period of interim single speeding definitely converted me to a SS/fixed fan and I'd echo many comments and thoughts already added here and in Will's blog post.
I now mix fixed and SS to a great degree and similar to Andrew, I also enjoy SS freewheeling on some of those longer/hillier rides (when time permits for more adventurous outings) and won't attempt to restate what he has already described so well.
One thing I will mention is when I did eventually try fixed for the first time, I found it to be equally exhilarating and nerve wracking, and kind of felt like re-learning how to ride a bike in a way, having never been directly attached to a drivetrain like that and unlearning decades of coasting habits! I now really enjoy the feel of fixed for much of my local riding and expect to keep it in rotation with 2 different flip flop wheels on hand.
To Patrick's note on using fixed cogs on standard freewheel threading... aren't traditional cup/cone bottom bracket lockrings the same threading (for the most part) and is there any value in using one of those for extra security or is the same direction threading pretty much render them useless vs. the force that may be applied with firm backpedaling? This is more a curiosity whether anyone has had success or failure attempting this... and I forget the name for it but the chain wrap around the bottom bracket trick I also recall reading/viewing somewhere to tighten or help loosen stubborn fixed cogs with wheel mounted and bike flipped over... roto-fix or something, was that it?
Brian Cole