Blizzard just added MoP to the default purchase of WoW. Great news, but who cares. Almost everyone's got it, right? Here's the fun part:
Trial accounts also have access to MoP. This means you can summon them to the Shrine and have easy access to all the cities. If you like taking things to the extreme, you could also take them to Timeless Isle.
Useless? Nah, it gets better. You can now use trial twinks to camp the rare treasures, like the Ancient Pandaren Mining Pick. Yeah, you'd aggro mobs like crazy, but you should be able to see it as ghost.
Unfortunately, (likely the best thing for trial accounts) pet battling still isn't enabled. Maybe it will be later. It would be cool to level pets between subscription times to sell.
If you can think of any other bonuses, feel free to post here.