If you haven't tried it and you have a gym membership, you should totally take a spin class. It is fun, fast and surprisingly not monotonous. It works well for me since it's in my house, and I can either get up early or spin when Gunner is taking a nap.
Getting back to the point--I need to log 500 miles this year, and I'm way behind schedule. While I hope that most of my miles will still be running, I am going to count some of my spin mileage as running mileage (cheating? maybe, but it's MY goal!) Spin bikes do not tell you how far or fast you go, but I'm quite certain I spin far faster than I run, so I think a time equivalence is more than a fair way to count spinning. I have decided to count every 30 minutes of spinning as 2 miles. I usually run more than 3 miles in a half hour, but I still want my goal to be challenging, so I'm shorting myself on spinning mileage to force myself to continue running. I log most of my workouts, so I have a pretty decent record of how much I have ridden my spin bike so far this year. I am adding 16 miles to my counter tonight to represent spinning miles. I hope to get a little running in this week, but I know I will definitely spin! I'm still behind on my mileage goal, but getting closer!