The wikipedia page for D-star is pretty interesting: http://en.wikipedia.org/wiki/D-STAR
I don't think I was aware that it was created as long ago as it was. It started as a research project by the Japan Amateur Radio League in 2001. Also, apparently it's been used for at least one satellite QSO in 2007. I don't know how popular that is compared to analog modes but that's pretty neat. There's a D-star capable microsatellite that is suppose to launch this October, 2010.
I'm impressed in how low the data speed really is, and yet they manage to get decent audio through it. I guess the data stream runs at 4800bit/s. 3600bit/s is voice audio (with 1200bit/s forward error correction, so only 2400bit/s for the audio) and a spare 1200bit/s for other data. A different modulation technique can transfer 128k but only on 1.2ghz.
Pretty much the entire standard can be implemented except for the chip that encodes the audio to a data stream. This is a proprietary chip, only available in hardware form, and noone's allowed to make an open source implementation of it. There is an effort to make an open source audio codec but this will create digital radios that can't talk to each other. With such a codec you'll have a dstar radio that can't talk to icom based dstar radios, although you'll be able to transfer regular data just fine. http://codec2.org/
GB7MH has been able to use this to make a d-star repeater without requiring the audio chip. Decoding the audio isn't necessary for the repeater functions. It's still possible to fully handle the rest of the D-star features.
Some people have been able to build homebrew radios using the UT-118 DV adapter that was originally intended on being installed in Icom radios.
Honestly, all this technology makes me very excited. I refuse to buy into it with a proprietary licensed codec however. Ham radio these days is way too much a commercial, consumer electronics field. The usage of a proprietary codec really flies in the face of the hobby and I refuse to support it. Godspeed to Bruce Perens and David Rowe. Hopefully sometime in the near future an open source codec will exist. I wouldn't scoff at an Icom radio, or any other, with an open source digital voice adapter in the place of the UT-118 one.