So, let's start at the beginning. Gaiman and Pratchett write this book. Terry Gilliam options in and has been trying to get it made into a movie. However, you're looking at a LOT of great stuff being cut just to fit it into feature length, but this is a director who doesn't have the best reputation for meeting budgets and deadlines. It's been stuck in neutral ever since.
Last September, Pratchett and Gaiman were out on the town and they toasted something. No one would talk about what it was.
Terry Jones, also of Monty Python, has a "semi-official" website. Last week, it reported that he and his writing partner Gavin Scott were in talks to write a new version of Good Omens.
A few days later, Pratchett went up on stage at SFX Weekender and announced Good Omens was going to be a four part TV series.
Get that popcorn ready!