I switched to a single speed cross bike for commuting 4 years ago and wouldn't switch back. I even ride it on some of the club rides I go on with it geared cousins. It is so much easier and cheaper to maintain that my geared bikes and if you choose the right gearing hills, wind and distance aren't an issue. My Chicago commute was 15 miles each way, sometimes 25-30 if I was running errands. That said it isn't for everyone.

elad,
I wouldn't recommend XTR on a commuter, as posted earlier it is better suited to off road racing (those titanium cogs would be shredded on a commuter). LX or XT are essentially the same except for weight and cosmetics and will work fine for years if you maintain your bike. My wife's commuter has a mix of ten year old LX and XT stuff off my old bikes and it works great. If you live in a really wet environment I would recommend cartridge bearings for hubs and headsets, or just pack the grease into conventional bearings. It seems like all the Shimano hubs and headsets I have ever installed are light on the grease, so I always take them apart and re-pack them.

banerjek,
Switching to ss or fixed isn't brought about due to paranoia about shifters. People wax poetic about why they switched to ss/fixed, I do it for the reasons mentioned above and because I like the simplicity. Mostly the reasons are personal not technical, you either get it or you don't.