I got my RadarBox in June 2007 and it hasn't missed a beat in that time even using it on 4 different computers at a number of different locations including portable when I've been out and about. Sure, every now and then I get a glitch when I'm running a whole load of stuff on the PC, but then that happens with most of the software I run - Windows XP is fairly stable, but it's not foolproof!
My SBS-1 used to disconnect itself quite often for no reason at all and this was a fairly common problem seen by others. I would come back to it and all the aircraft contacts including those in the list would have disappeared. The only way around that was a PC shutdown and restart. I think that the majority of problems that people have with RadarBox are almost certainly down to the PC rather than the RB software/hardware as if there was a problem, I'm sure I would have seen it more as a common issue on the different PC's I've used.
Certainly, there was a "misinformation" campaign by the "other side" that attempted to put people off RB by saying that the software was unstable. This campaign didn't get anywhere as it just wasn't factually true. There have been very occasional hardware issues, as there have been with the SBS-1, but as AirNav are offering a 2 year no quibble guarantee (as long as you don't take the box apart) then even this isn't a problem.