If you have good grades, you don't need the damage control that a post-bacc provides. Some other reasons to use post-baccs are if you feel you need the formal linkages to med school some of them provide, or if you need the structure and support they may offer. If you do not do a formal post-bacc (I'm not doing one), you just have to make sure you get the other ducks in a row for yourself: volunteer work/clinical experience, good MCAT scores, and letters of reference from professors are things you have to consider.
Even enrolling as a non-degree or special student, your university's pre-med or career placement office may be willing to let you use their committee letter service, if there is one, or their reference letter forwarding service. The latter allows your letter-writers to send one blind letter to that office. The office then sends it out to whatever schools request it so that you've never seen the letters and the letter-writers don't have to send a letter out to every single freakin' school you apply to.
