I just bought PrinterShare yesterday. Google's cloud print has always been pretty flaky for me, where things wouldn't print most of the time until I went back to my laptop and restarted Chrome.
So here's my 2 cents so far:
Aside from the steep $12, PrinterShare connected fine to my Canon MX870 via WiFi, and pretty much worked. I say pretty much because the only (2 page) doc I've printed so far, printed the first page only, and the % status on the ATP showing page 2 being transferred hung half way, before timing out with a connection error.
Eventually I went over and found the printer was somehow hosed - the WIFI light was blinking and hitting cancel on the printer it just stayed in some kind of "please wait..." state. So after 5 minutes I power cycled the printer, and tried a second time to print just page 2, which immediately worked perfectly.
So too soon to tell if it was a one time deal, a fluke w/ the printer's connection to the network, or some mismatch with PrinterShare that will cause the same problem in the future.
All that said, it's the best wifi printing app I've seen so far, so I'm giving it the benefit of the doubt that it will work as needed (since I'm already out the $12 anyway