A generally overplayed complaint is poor signal strength at the Roku Box. After thinking this over and looking around I found the solution in a relatively inexpensive router made by ASUS called the RT-N12 which sells on Amazon for about $40. It has a switch on it which gives you three options...Router; Access Point; Repeater.
I was having trouble with my neighbors in a large Manhattan apartment house (I can see 40 other networks) and three walls constructed of plaster on wire lath in a steel frame and concrete building do not help. Along with judicious choice of wifi channel, and careful placement of the two Roku boxes, I could get fairly acceptable results most of the time. However recently a new neighbor appeared, and almost blew me away. Using my laptop I realized he (or she) had two MAC addresses on the same SSID.
I Googled repeaters and found the ASUS, along with a lot of information in the dd-wrt wiki which made it simple to set up and install. I get 15 MBS from the cable company, but with a single Router I never got more than 3 or 4 on the wifi signal. With the repeater I now can measure at least 12 or 14 next to the Roku boxes and it goes without saying that Netflix, Amazon, and anything else in HD plays consistently without buffering or interruption. No doubt the wire is the best answer but there are many times when it is impractical. Not all of America is housed in single family homes.
Obviously a laptop or IPAD is essential for the best results.