Gregg prompts me, appropriately, to share my experience of spinning, having teased you with my intentions earlier.
I did go to the spinning studio in Newtonville (Spynergy) ... it is great, and the people are lovely. However I just did not enjoy the experience. First I was on an upright bike (I love my Strada), and find those awfully painful saddles as bad as their reputation. Second my legs are fairly strong, so I needed to set the tension up a little so that I wouldn't bounce around on the bike. However with that amount of tension, and the spinning cadence (speed) the instructor suggested, I found myself out of breath very fast, and indeed a little light headed. After that I slowed down considerably, but of course was not really in synch with the class at all.
Now I go back to the question of whether I should just get a good recumbent exercise bike at home. If I would not really "keep up" with an instructor in a spinning class, perhaps having the option to exercise at home is better - more likely to hop on the bike more often. Anyway, that's where it stands right now. The Spynergy people emailed me after my first, not great, experience offering another free class to encourage me to stick with it, and I may yet pluck up the courage to try again.
Meanwhile I have been back on my trusty old Nordic Track for a few sessions, just to keep up some form of exercise, but this is a problem yet to be definitively solved. Watch this space for more news as it unfolds.