DAllegro is for Allegro 4.x, go here if you need D support for Allegro 5.
DAllegro and DAllegroGL
A bunch of examples, plus a larger demo game is included in the DAllegro download. They are all direct ports of regular Allegro's C versions, and are primarily used for verifying that DAllegro works. They are obviously not good examples of D programming. A basic Tetris clone (DBlocks) is included as a better example of a D game using DAllegro.
All of Allegro's examples, the demo game, and the tools and tests that are ported to DAllegro, seem to work perfectly. Performance is on par with the C version. The platform-independent parts of the API are completed, so are the Windows, Linux and OS X specifics.
DAllegroGL hasn't reached the same level of maturity yet, and is only properly tested on Windows, and using the DMD compiler.
Tango and Phobos
DAllegro is compatible with both Phobos and Tango. DAllegro 188.8.131.52 should work with Tango 0.99.3, 0.99.4, 0.99.5, 0.99.6, 0.99.7, and 0.99.8. Later versions than 0.99.8 have not yet been tested. DAllegro SVN is compatible with Tango 0.99.9 and DMD 1.061, but support for Tango older than 0.99.8 has been dropped.
The latest compiler known to work with DAllegro 184.108.40.206 is DMD 2.026. DAllegro in SVN is updated to work with DMD 2.047. Currently you need to build with -d, which makes the compiler accept the now deprecated volatile statements. The plan is to someday replace those with atomics.
Support and feedback
DAllegro has now got its own forum. For questions not specifically about DAllegro, you'll probably get more replies at the Allegro forums. Most how-to questions about DAllegro will have the same answers as for regular Allegro.
If you've found a bug, creating a ticket is the best way to report it.
For the most part, you can just follow the Allegro docs. They are available in various formats here. You can also find tutorial links, etc. at that site. The differences between DAllegro and Allegro are noted in the readme file, which is included in the zip download.
If you're not on Windows, you can download the Allegro source here. There are some Linux binaries too.
SVN log: http://alleg.svn.sourceforge.net/viewvc/alleg/bindings/dallegro/trunk/?view=log