i'm not exactly sure what the formula is for how much experience a sub-90 character gets for winning a pet battle, but i know it scales with both the character's level, and the level of the pets in the battle. as a result, a level 30 character battling level 9 prairie dogs in the south barrens doesn't get a lot of xp - probably less than she'd get herbing kingsblood. which brings us to this guy:
it started when she had me log on to her second account and fire up her baby monk. meanwhile, she got on her level 90 mage and opened a portal to pandalaran. once there, she transformed into her sandstone drake and i had the monk hop on. a quick stop at halfhill to pick up the flight path, and then a little hop over to the west, to the "dead zone". there's a nice big swath from farmer nishi over to the swampy plateau behind the area where old hillpaw keeps losing his chickens where there are oodles of critters but no hostile mobs. none. zip. and winning a pet battle against level 23-25 pets when you're only level 30 gets you more than a tenth of a level. in just a couple of weeks of occasional playtime she managed to get her monk from 30 to 60. so i asked her to transport my little rogue over as well. and he's picked up ten levels so far.
every now and then i'll stray a little to close to the edge of the dead zone, and a wolf or a vermling will have himself a nogglesnack. and sometimes a high level character will do a double-take and ask "you lost, little fella?" but mostly it's just a quiet and relaxing way to level yet another alt.