I have a whole bunch of bikes, because I like working on bikes and riding different kinds, but even so I think it's a good idea to have more than one if you're going to commute - for an emergency backup if nothing else. I actually have multiple 'commuter' bikes, they're all set up for different uses (primary, winter weather bike, cargo hauler), but all are cheaper, less flashy bikes than the ones I typically reserve for recreational use*, that way I don't worry so much about theft or exposure to the weather when I lock them up in front of my workplace. Another difference is that I have racks and fenders on all my commuter bikes, but not on any of my recreational bikes.

*-of course there's some overlap, I use my 'commuters' for fun rides on a regular basis and once in a while I'll ride a 'fun' bike to work if I'm just going in for a short shift and am planning a longer ride afterwards.