If you are currently running iOS 4.35 you won’t be able to get a untethered jailbreak until iOS 5 is released. Why? Various jailbreaking teams are wanting to hide their exploit so Apple doesn’t patch it in iOS 5. This will allow a jailbreak for iOS 5 to be released almost immediately whereas if the exploit was patched they would have to find another exploit which could take weeks.
Another jailbreak specifically for A5 devices is being held from release as it is a bootrom exploit. This means it cannot be patched by software as it is a hardware exploit. This is being saved for the iPhone 5 (and maybe the iPod Touch 5G) which are rumored to have an A5 processor.