The Pre - I've owned this unit for about three years now. It get's used on every project I track. It's the API sound. What more could you want? When tracking drums, it usually ends up on kick and snare, but you could put it anywhere and it would sound great. It works well with ribbons, condensers, and dynamic mics. It's a really good vocal pre, but won't work for everybody.
The AD - the conversion is top notch. I have SSL, Focusrite, DBX, and Digidesign converters. The API are among the best. And you can adjust how hard the converters are hit, separate from the pre, so you can really drive the pre (which can sound fantastic on some sources) and not peak your converters. Great feature.
The Routing - this is one of my favorite parts about this piece. You can patch into just the converters, allowing you to run through more analog gear, and back into the API for conversion. It's very versatile.
the downside - I have no idea why, but most of these units shipped with superclock instead of word clock. You can ship them back to API for an upgrade to word clock, but it's ~$300. Having only superclock can be a real pain, if you're trying to interface with other digital gear that only has superclock. This is the only reason I didn't give this unit five stars. Other than that, this has everything you need in a preamp/converter.