Update: Apple has now stated that they will patch the hole in the next few weeks. Source: Yahoo
Security researchers are warning that due to the exploit that JailBreakMe.com uses we can quickly expect malicious hackers to develop back doors to modify and install malware on your IOS devices. This impacts any iPhone/iPad/iPod Touch that is running the latest version of IOS 4. Hackers could find ways to steal data from non jailbroken products that run IOS such as passwords and documents. When asked Comex who developed the tool to JailBreak the latest IOS stated that Apple may deploy a security update soon. The next version of IOS version 5, includes safeguards that do not allow loading of custom rom’s on the iPhone unless they’re specially signed by Apple. So if you upgrade to 5.1 only certain flagged builds of 5.0 would allow you to downgrade.