I can vouch for that as well. It can feel over damped when you come to it from say a Fox damper and it really is best mated to a Devile fork IMO; that pairing makes everything feel 'harmonious' i.e. both units are working in the same way, metering out the same amount of squish in response to the input and so keep the bike balanced.
I can imagine a Vipr mated with a Fox or RS fork might make the bike feel nervous or unbalanced (whereas the Devile can I think be used more successfully on its own).
I'm not sure that over damped is how I would phrase it - with the Vip'r, it seems to me that the air spring has a very different characteristic; in my experience Fox shox blow through the mid-stroke (an issue that is exaggerated with high volume air cans) - like a switch from rising rate at the sag point to linear or falling rate mid stroke, then a switch back to rising rate towards the end. Normally i would argue that this is down to suspension design on my bike, but given ive found this on every fox air shock i've used, i'm more inclined to think its just the Fox characteristic. Perhaps Fox are aware if this hence the boost valve..? As a dyed in the wool bike tart, my experience with Fox is on most suspension formats: single pivot, linkage activated single pivot, Gt I-drive, URT, and currently a Nicolai Horst link 4-bar.
In contrast, Bos seems more stable/predictable/linear... Difficult to explain but there's just no surprises. The damping feels constant throughout the stroke, but I wouldn't say "over damped". My first experience of Bos suspension was my 1st set of Devilles. Coupled with a CCDB I believe that for a gravity bias it was the best suspension set up I've tried. Based on being impressed with the Devilles I bought a Vip'r - I've now sold the CCDB, which says a lot for the Vip'r in my opinion.
I would love to have a suspension engineer take some Bos products apart and explain the difference. The only product that comes close (well, as good in my experience) is the marzocchi Rc3 damping system.