I agree it is a huge benefit to be able to access different map areas with ease and speed. I didn't play Reach as much as I would have liked to, and was wondering if some of the crazy overskilled players ever figured out another use for it.
"mad cuz got black-jacked? I coined that, you all were here." - RUNwhenCOPScome, on Black Hat and Care Package controversies.
Well, I saw one guy use it in a trollish but surprisingly effective way on Haven once. It was an Oddball game, and he jetpacked straight into the ceiling while he had his teammates around. That helps divert shots - it's easier to shoot two people side by side than it is to shoot one guy that's essentially standing on top of another. Enemy fire gets drawn away from someone, but you have to do it strategically - generally when surrounded by teammates. Someone can get the jump on someone, basically. Just don't be that guy who jetpacks straight up by yourself into the line-of-sight of the entire opposing team.
Also, you can jetpack up along doorways to hide your head. I've done that a few times - it can be the extra second you need when you're getting team-shot to get away and recharge your shields.