It's nice to have shiny new equipment but for something as specialized as discs, they're pretty costly up front due to the low production volumes, more difficult to sell due to limited market and don't have great resale value.
Sorry Wasfast, your helpful post could have done with out this, in my opinion none of what you have said in the above quote is at all accurate.
Out of a company like Zipp's product line I would have though the discs outsold quite a few of their other wheels, not all of them but not at the bottom of the sales sheet. You'd only have to count the number that have been rebadged in professional racing to indicate that they are well respected and widely used.
With regards to the OP question, the Zipp disc is a known quantity, loads of people have them and they are truly 'tested'. I have had three 900's over the last six or seven years and never had one fail. The hubs are good and easy to service.
Having said that there isn't an area of them I couldn't point at and ask for better. The valve cut out could be larger (IIRC the newer one I have has addressed this, possibly worth noting if you bought a older used one 2nd hand). The hubs are not the latest of greatest in Zipp's range on the 900 disc -Off the top of my head I believe the 900 uses an older design of hub, not sure if or what the problems of this are, I do prefer working on my later 188 equipped wheel sets-. I could be wrong on this!
So like I've said the Zipp's are a solid choice, not the cheapest but I think you're unlikely to have any headaches with them.
I'll explain why I had three because without doing so my claims of them being a solid choice do look a bit suspect
The first 900 was kept for four years and I wanted a newer version because I had used it A LOT and it was starting to look a bit tired so when I got offered a good deal I sold it.
The second one wasn't as true as I would have liked and I started to think it was getting worse. I now don't think it was getting worse because having bought a third one it was exactly the same, so that error lost me some money but I did get a newer disc with a larger valve cutout which is of some help.
I would like to buy the new Lightweight disc because all things being equal it is lighter. But, I have never worked on a LW disc so they may have some draw backs. I currently have a set of 808, 202 wheel sets along with my 900 disc, I have had two sets of 404's so I have a lot of experience with Zipp hubs and could service them blindfolded as well as being able to exchange parts if something breaks and I can't get a spare in time. Thats my reasoning for sticking with Zipp so far, any slight possible advantage to be had with another manufacturers wheel set isn't as important to me as simplicity of servicing, knowledge and only needing spares for one brand.
Hope that helps you a little