My wife and I have done this a couple of times. Not really sure why other than to see what it felt like. I kind of enjoyed it actually. My head is really sensitive but with the condom on she was able to play with the head more without tickling me. Plus sometimes I guess I'm a little too salty for her tastes and with the condom on she was able to keep sucking through my orgasm which was also very pleasurable for me.

The flavored condoms worked well, and so did the unlubricated ones. Condoms with spermicide would just be a bad idea all around.