i'm sure most would agree that getting the cracked apps is probably the best benefit of jailbreaking. i'm very new to the itouch as well. i'm pretty computer saavy. that being said, it took pretty much a whole day to learn and then jailbreak the new 4.2.1 ios. i'm one to learn as much as possible first. i haven't looked in the last couple of days but the biggest drawback is the fact that it's a tethered boot. at least for now. this means that if your battery runs down, you'll have to boot the device with the aid of a computer. it won't power up even after you recharge the battery. this is quite a headache if you're not at home. there are a lot of resources on jailbreaking. do yourself a favor though and read up on as much as you can prior to actually doing it. i would backup and media (photos and videos) before you take the plunge.
with jailbreaking you never have to worry about paying for a useless app. there are so many that it's hard to truly know what is good. i figure this would be worth it alone.