I had an old Roku XD in my bedroom but, when Roku added PBS, it turned out their programs were incompatible with my XD. (The explanation of the incompatibility is interesting in its own right -- See this discussion and this post from Roku for the details).
I had gotten my money's worth out of that old Roku and also wanted the remote headphone feature and faster processor in the newer Roku 3, so ordered one.
When it arrived, I installed it and settled back to watch TV, but it went through the menus more slowly than the old XD had and I began seeing pauses for buffering, which I had never seen with the XD.
I checked the signal strength using inSSIDer and saw that it vacilated around -60 dBm as shown in this two minute sample:
It was not robust, but the old Roku XD had functioned well with that signal -- could the new Roku radio be less sensitive than the old one?
I had been meaning to return my ISP's WiFi router/radio, so I purchased a new one and was happy, but surprised, to discover that the Roku 3 worked well with it. I checked the signal strength with the new router/radio and found that it was more stable over time:
and, as shown in this overlay, a little bit stronger:
Neither is a "five bar" signal, but my old Roku works with either. I may have gotten a bad Roku 3 (Roku is willing to exchange it, but that would leave me without TV for a week or so) or it may be that the radio in the newer model is less sensitive.
Regardless, it would be helpful if radio sensitivity were included in product specs and reviews -- by Roku and any other WiFi device manufacturer.