Yes, I have. To me, it's no different than geocaching in your car. The vehicle only gets you close to the object and then, you go on foot. I used a Garmin GPSmap 60CSx which was RAM mounted but battery powered so I could take it with me once I was off the bike. My interest in doing this was brief but it resolved my curiosity.
I do it all the time.
Just found three on Friday, I played hookie from work,it made it up to the 70s and I just had to ride. Caching on the bike is fun because I get a chance to ride different roads I don't normally take.
I take the family out to geocaches it's fun to watch my 10yr old daughter find them. Sometime they have kids caches listed. It's a good activity just get out of the house and get some air.
I've been Geocaching for over 10 years now. It's a fun activity but it's kinda sad how many are out there. I only own one, but some people own many so it's hard not to accidentally trip over them. I do it at work, in the Jeep and on the bike. There's a great phone App for it but you need signal for it to work. It's a fun activity and gets you out walking around.