My handy-dandy little Western Sod reference 'book' says not till after May 15. For Bermuda not overseeded with rye, it says, "Remove thatch when more than 1/2" thick. Aerify as needed during the first four weeks of summer."

You can also use the Master Gardener Manual chapter on lawns for information on Bermudagrass maintenance including dethatching. There is no need to dethatch unless the thatch layer is greater than 1/2 inch. It's a pretty stressful process on your lawn so be sure to allow for at least 4 weeks recovery time.

Here is a link that might be useful: Arizona Master Gardener Manual

Verticut is the way to go and now is the time. Follow up with fertilizer and water more often for the first couple of weeks. You will need to rent a machine to verticut. Not the same as dethatch

Hmmm... Interesting discussion, especially as we always wonder if we should dethatch around this time of year. We end up just wondering and never doing. However, our grass does feel "like a sponge" so maybe the verticutting would be a good idea. Not that I think we're going to get around to that, either. :O)

Here is a link that might be useful: Verticutting

THANKS! To all of you for your comments and useful links. Greatly appreciated!