i dont protect mine at all... 320gb sata desktop drive. there is constant error-correction going on, and the drives themselves are rated for g forces well beyond any bump youll hit. dont worry about it, at very worst your computer might seem a tad slower because its waiting for the harddrive to recover, but youll never really notice it.
careful about adding protection too. you dont want to overheat your drive and you dont want it loose enough to oscillate, which would end up being worse then just mounting the drive normally in a fixed fashion.