iPhone Atlas claims that while the jailbreak method for 1.1.3 has reached a state that is suitable for end users, the developers of the jailbreak are still debating whether or not to release it ahead of Apple's official SDK release.
There appears to be some limitations to the 1.1.3 jailbreak, with applications running in "restricted user mode" meaning that the popular Installer application will not run properly in its current form.