The Digi 002 is an audio recording interface to be used with a computer and software DAW. It has 8 analog inputs (4 with mic pres), ADAT input, S/PDIF and RCA input. It also has 8 analog outputs. This aspect alone has been valuable to me because I sometimes take the 002 to gigs to use as a headphone mix for a bunch of musicians. Having all these outputs is essential.
I have always used the 002 with Pro Tools. Although, on a previous computer I also used it for all CoreAudio applications ranging from Safari, NI stand-alone applications, iTunes/iMovie, etc. Originally I purchased the 002 because I wanted to record a full acoustic drum set in my studio. I made use of all eight analog inputs and even the ADAT inputs when I went a little crazy with microphones sometimes. Over the past several years, I purchase a e-drum kit so I have just been using the MIDI in for drums. Same goes for piano. I use the s/pdif input to run electric guitar and bass direct from a Pod HD through the 002. I only really ever mic up vocals and acoustic guitars. I don't really need all the inputs now for the way that I record, but they are good to have nonetheless.
I use the 002 rack with a Mac computer. Installation was pretty easy, but I could not speculate about installation on Windows and having to worry about drivers. After that, it is pretty much plug and play. All the inputs show up in Pro Tools and have worked without any problems. I have used the inputs - XLR, analog, ADAT, S/PDIF.
I have owned this hardware for six years. I use it everyday in my studio. I have never had any problems with something working incorrectly in the hardware. I have had to purchase a new computer several times since I have owned the hardware. Installation was not a problem. Even though my computers have gone out of date, the 002 rack does everything I want it to. Sure there have been nev hardware release by Avid over the last six years (003, Eleven Rack, Mbox 3, etc) to be used with Pro Tools. However, this hardware is reliable and does exactly what I need it to do.
Someday I will need to replace this hardware. This hardware will not be officially 'supported' in PT11 (although, I continue to happily run PT8). I suppose it may stop functionally working in the future, too. As of now, I think I would replace my 002 with a UA Apollo.