Look, I'm all about jailbreaking, but to indicate there are NO drawbacks or risks and no stability issues is just not true...
Within 24 hours there have been widespread reports of the Weather app not working (no big deal I agree, but it's an indicator that stuff gets broken), and people are having issues after installing basic tweaks like SBsettings with the phone being stuck on the boot logo after a restart.
That kind of stuff may be no big deal to an experienced JB'er who can work around the instability issues, but if you are an average user that might not bring their entire computer with them everywhere to "just do a restore" when something like that pops up, it can really ruin a day.
When I jailbroke the original 2G (using jailbreakme), it locked up on me during a business trip. I had no phone and no way of restoring. That has NEVER happened on the stock firmware for me (and even though I'm sure it has, it's much more rare on stock than on JB firmware).
Jailbreaking is cool. It lets you pira... errr... customize lots of stuff, steal tethering from AT&T (violating the contract you agreed to), and lets you do lots of other things too.
I think it's sorta worth it when available, but not nearly as needed as it once was.
And it DOES void the warranty, even if you lie about it later when you need it (because that's what you're doing if you take it in for warranty work, lying about it being jailbroken, even if you restored it after...).
Is it worth it? To me, yes. But I'd say probably not for the vast majority of "average" users. If you want to, just know that the "there are no drawbacks" statement is a bit of a lie. There are. Some less annoying than others, but there are.