my 1975 750K was my main means of transportation for several years. Now it needs gaskets and has a slight oil mist when I ride. Since I work in an office I can't show up with my pants all greasy so I have taken to riding my 1973 750 as the daily driver instead. However....
...In my nearly 10 years of ownership my 1975 cb750 (which racked up about 50K under my arse) proved to be more reliable than my 1995 wrangler, which i bought new in 1995 and now has approximatley 114K on the clock. Maintenance costs, fuel expenditure, insurance, has all been much much cheaper. I have had to put a tranny in the jeep, but the cb750 motor never needed to come apart until last year when the valvecover and base gaskets both started to weep at the same time, it has needed a new seat, a couple of brake light switches, parts to fix the crash damage, a caliper rebuild, and several speedometers but all in all that still cost less than my junkyard tranny for the jeep (which I installed myself). In the entire time I have owned the cb750 she has never failed me or left me stranded. Even when I chucked her down a highway at 60mph I was able to pick her up (despite the broken foot and collarbone) and start her up. So far my 73 has given me the same reliability this year.
So is the bike reliable? yes....but there is something more to be said for gear you own in going "bike only"
I live in NYC, which has one of the best public transportation systems in the country. If I don't feel like taking the bike in to work I can hop a subway and maybe all I lose is 15-20 minutes on the commute (the train takes longer). I work a white collar job in an office so there are days where I don't think I can get away with riding in in a business suit in the rain, so I hop a train and arrive none the worse for wear. If you live in an area where you can sometimes rely on public transit then going "bike only" is fairly easy. If not then it depends - if you need to be dressed up for work you will need a good rain/riding suit and a way to carry a second pair of shoes. If not then there are other concerns, most of which a good backpack and saddlebags can cure.
I guess my point is there is a lot more to think about when it comes to going bike only than is the bike reliable enough.