If you have previously jailbreak your iPhone 3G with PwnageTool 2.0.1 considering not updating it on the new release of Apple iPhone 3G firmware 2.0.1. This could loose your application installed previously courtesy of the tool.

The Dev Team have an explanation on the current situation on the tool on their blog here.

3G owners can in theory update, but you’ll lose the jailbreak, and you should only carry out this update if you always plan to use the 3G phone with the original carrier, but be warned that there is a baseband update that occurs during this update that could impact the ability to unlock the device (if and when an unlock becomes available), we have not fully tested this baseband update as yet, but we think it is better to be safe than sorry, officially unlocked SIM-Free iPhone 3Gs will always remain unlocked with the updates you apply from Apple, but again the jailbreaks will be lost.

So basically it does not support the current build of Apple iPhone 3G 2.0.1. Few points they have emphasized on their blog.

* If you own a first generation (2G iPhone), no matter what you do now, you don’t have to worry, the next PwnageTool will get you where you want even if it you prematurely updated. 2G is completely pwned at every conceivable level and you’ll always be OK. But if you own a 3G iPhone and are looking for unlock in the near future, don’t use Apple’s update yet!
* If your 3G iPhone is on a regular contract and you always plan to be with the carrier then you can update but you will lose the jailbreak and access to third party (non AppStore) applications.
* If your 3G iPhone is not on a regular contract and you plan to use it on an alternative network to the carrier that supplied it then do not update unless you do it with the impending PwnageTool update.
* PwnageTool v2.0.1 does not work with version 2.0.1 of the iPhone or iPod update from Apple.
* We will release an update to PwnageTool when the testing has been completed and all applied changes have been checked for safety.

via engadget and appleiphoneapps.