No.
Jailbreaking breaks your warranty.
If you damage your iPhone, Apple wont fix it. Some of my friends have damaged their jailed iPhones and gotten full replacements! This is not a possibility for someone with a jailbroken iPhone. Apple will just say, The reason its not working is because you hacked it. Hacking your iPhone is not sanctioned by Apple, so whatever you do is at your own risk.
Theres always a possibility of something bad happening.
Even Zibri says, ZiPhone has worked reliably for many iPhone users, but occasionally things do go wrong. If this happens, you could be left with a iPhone that is unable to restore. This happens because something in your iPhone so so corrupt that either iTunes cannot read your it or pressing restore just wont work. Also, you have to be really careful when new firmware comes out. If you upgrade
Its dead.
The apps are not that great.
A majority of the iPhone apps on installer are absolute pointless. Also, people make a lot of apps just to prove the point that it is possible, but actually do nothing helpful for the user. I have two examples. I downloaded this one apps called cowbell
You tap on it and it makes a cowbell noise, this is self explanatory. There is also an app that lets your record videos, but only 5 seconds long. Then, the only way to get it onto your computer it to SSH into your iPhone. Trust me there are a lot more apps that do nothing helpful than apps that cool or help you get things done.
Your iPhone works fine as it is.
You love your iPhone and it already does everything you want it to. You just have to live for 4 months, knowing it can do so much more. Its a great iPod, a great phone and a great internet communicator. Why should you jeopardize that?
The iPhone SDK looks amazing, and its coming in 4 months.
We already saw the power of what companies could do in 2 weeks with the SDK. There is nothing like those apps in installer. No Touch Fighter, no Super Mokey Ball, no Spore. Come June, you will have all of that. Its worth the wait.