Apple fixed the PDF exploit with iOS 4.3.4 which was used in the cable free jailbreak method : jailbreakme.com.
What you have to do? :

Head over to TinyUmbrella  immediately and save your SHSH files. If you haven’t heard of  TinyUmbrella before, all you have to do is download the corresponding software for your PC/Mac and plug your iPhone and ‘save’ your SHSH files, simple!  This is highly recommended for all iPhone 3GS, iPhone 4 owners.

(Or)

Launch Cydia on your iPhone and make sure you have your SHSH files saved over there [You will …

Apple released iOS 4.2 for the masses finally. While it does some nice things on an iPad, there isn’t much for iPhone 3G/3GS/4 if you are happy with the current jailbreak+unlock.
You are urged to download TinyUmbrella and save your current firmware SHSH files. It is available on multiple platforms (Linux, Mac, Windows). The SHSH window for signing your firmware version is almost closed, so better hurry.
Cydia for 4.2 firmware doesn’t even work the traditional way, nor is there an unlock available as of this writing. So, kindly ignore the iOS …

Apple just released iOS 4.1 update, not a super important update for 3GS users (unless you are into GameCenter!). iPhone 4 users can finally relax given that iOS 4.1 comes packaged with a fix for those nasty sensor issues.

Before you do any thing, please quit iTunes and do the following. TinyUmbrella is what you need to save your iPhone from Apple’s anti-jailbreak updates.
Download TinyUmbrella for your Mac/Windows/Linux.
Install/Launch TinyUmbrella and save SHSH blobs for iOS 4.0.2 for 3GS, iPhone 4 from Apple (or Cydia after the SHSH blob signing period by …