Hardly ever. Bought a cheap Singlecross from the LBS over 10 years ago as a stopgap, still commuting on it now. Previous commute bikes have generally been fairly long-term (parts get replaced, and I did have one commuter where I replaced the frame and most of the parts except the stem, bars and seat post). When racing I bought parts and clothing more often, but bikes not so much- and I still have my 'cross bike, the 1" steerer might become a bit of an annoyance in future but currently parts easily available.