This is a very interesting thread (to echo a previous post!). I've had many very involved hobbies: SCUBA diving - dove 2-3 times a week, but when I left Okinawa in '78 I sold my gear. Miss it sometimes, but not much. Motorcycles have been an off/on addiction since 1966 - don't own one now but definatley get to jonesing at least once a year. Bicycling was "serious" from about '81-'91 but once I sold my Colnago I got over it. Have had some various recreational bikes and am getting back into commuting in December when my office moves...we'll see how this works out.
Current "burn out" is competitive BBQ competition. I've got my Kingfisher rotisserie in the side yard. I use it fairly often but only get out to competitions 3 or so times a year...fun but I wouldn't miss "it" if I quit -- I would miss a lot of the folks, though.
So yeah, we all go through cycles -- I forgot to mention my catamaran sailing period -- got in cheap, had fun, sold the boat -- came out pretty even so that's a VICTORY in the world of boating!!
I'm looking forward to getting back on the bike regularly -- I do miss dodging cars and sliding on my various body parts in rainy weather.