@pandabear: You're buying convenience and cosmetic items. 10% more XP. I imagine things like re-spec potions, gold/xp/whatever game rep or currency boosters, bags, stuff like that. Guild Wars had costume slots where you could put costume items (Lots purchased) into those slots and it'd override the look of your current gear. I'm sure they'll add in lock boxes. Like Sheogorath's Crazy Box of Crazy stuff! I think they also mentioned additional areas to adventure in and stuff, too.
Old Republic isn't really no strings attached free to play. There are so many disadvantages to not being a sub that by the time you're off the first starter planet, you're fighting an uphill battle. If you want to play another class to see the story, if you're not a subscriber, you'll need the patient of a saint to level up those alt characters.