I end up changing it 2 or 3 times a year, depending on how much I ride that year. Twice is minimum, though. By mileage, I change every 5K to 6K miles. I'm in NH, so I do have to store it for the winter, and it does get cold out in late fall and early spring.
I ride a 1993 Ducati M900 Monster, typically about 11K to 12K per year. I change in the fall when it starts getting cold to full synthetic 10W/40, ride for a month or two and store it with that for the winter, ride for a month or two, then change when the weather starts to warm up to the originally recommended full synthetic 20W/50 for the main riding season. If it's a high-mileage year (15K to 18K), I'll do an extra change during riding season. I've got 260K now, on the original engine, so I'll say this is a workable program.
My wife has a 1995 Ducati M900 Monster, very similar to mine, but she rides more like 2K miles a year, and only when it's nice and warm out, so I change her oil once a year, and keep the recommended full synthetic 20W/50 in it all the time.
1993 Ducati M900 Monster "Patina" (259,000 miles, so far) -- 1995 Ducati M900 (wife's bike) -- 1979 Vespa P200 (daughter's scoot) -- 1964 Vespa GS160 (160cc 2-stroke) -- 1962 Maicoletta scooter (275cc 2-stroke) -- 1960 Heinkel Tourist 103A1 scooter "Elroy" (175cc 4-stroke)