bontrager XXX hubs

The Bontrager hubs used in the Rhythm and RXL wheels (that look very similar to the hubs in the XXX wheels) are quite a basic hubset.
As mtbbiker72 mentioned, they are made by Formula, as oppose to DT Swiss that made some of the hubs for Bontrager prior to 2009.
This I assume is a cost-cutting measure, as the DT stuff isn't particularly cheap. Bit of a bummer since the DT stuff is mostly bulletproof.

At our store, we have experienced issues with the freehubs of two wheelsets out of about 13. This was very early in the season (over 12 months ago) and was denoted as a loud "pop" from the freewheel when putting down power. It was due to a machining fault and I believe was an issue with earlier batches.

The awesome thing about Trek is the warranty they have with their wheels - 2 years, and we had a super quick turn around with getting a new wheel in for the customer.
The higher-end wheels are also built in their US factory, and from our experience have been built and tensioned very well compared to other brands factory-built wheels.

The hubs themselves are simple to take apart and service, though are not as well-made as other high-end offerings on the market. I would personally put them at a similar quality level as Mavic hubs, but I'm sure others will chime in with opinions on that note.