After a false start earlier in the week, Diablo III will properly enter open beta this afternoon. It's only for stress-testing over the weekend, though, so get your robe and wizard hat laundered sharpish or you'll miss it.
The open beta weekend begins this afternoon at 12:01pm Pacific, then will run until 10:00am on Monday, Blizzard explains in a Diablo blog post. All you need to play is a Battle.net account. You can download the client in advance, so you don't miss a second.
The beta is relatively small, packing the first part of Diablo III's first act, but you will be playing Diablo III. Unlike proper closed beta testers, open beta players won't receive 'Beta Bucks' to spend in the auction house and cannot post in the beta forums.
Diablo III launches for PC and Mac on May 15. The closed beta test will wrap up on May 1.