I have a 40 mile commute that I do a 2-3 times a week whenever the temps are above 20F. For a couple years I owned only one bike for commutes, group rides, and tours: a Fuji Absolute 3.0 hybrid. It came with an adjustable threadless stem that gave me a wide range of riding positions depending on what type of ride I wished to do, and an easy swap out of tire widths/treads gave me even more versatility. Last summer I purchased a nice road bike for group rides, and made my old hybrid into a dedicated commuter/touring bike. I replaced the flat bars with a nice northroad style and Brooks saddle to make it even more comfortable for long rides. I enjoy having these options, but truly it depends on your budget whether or not you can justify having more than one machine. For me having the proper tool for the job is important for my enjoyment of the sport. (Not to mention the fuel savings of my commutes come out to roughly $6 a trip, so I feel more than justified in indulging my passion.)