At this point, an upgrade to 2.0 is not urgent for iPhone classic owners who use a lot of installer apps, because most of them have not been upgraded to the new OS version, yet. But there is one case where it's advisable to upgrade, and that's if you want to sell it. Only version 2.0 has a safe delete feature with which you can remove safely all the information you've put on your phone. If you don't do that, the buyer can get access to all your info quite easily. So, for once, it's seller beware!
myPhone to go
As of yesterday, I'm a happy owner of a black 16GB iPhone 3G with an Orange plan. That's why my "old" one (after all, it's all of three months old) is now up for sale here, and it already finds quite keen interest. Which is unsurprising because I've pwned it (there's a new word for you!) for OS X version 2.0 with the Pwnage tool and paying close attention to this and this indispensable tutorial. The procedure is not as fool proof as Ziphone's (which is not available yet), but that's less a matter of IT knowledge rather than of dexterity in hitting the right buttons at the right time ... good luck!