This has been acknowledged by @Musclenerd in responding to a question by his followers on Twitter. These hardworking folks are working on a fix, so let’s hope this can be resolved soon.
If you cannot wait, you can opt for baseband chip replacement service or hardware downgrade. If you prefer DIY, you can purchase a baseband chip here.
UPDATE: We have heard from iPhone 3G users that they were able to restore the GPS functionality after downgrading to iOS 3.1.3 (still with baseband 6.15.00).