FWIW:
*I don't use the keystones, I use what are called "biscuit jacks." I get them for about 50 cents each (in quantity) from DeepSurplus.com (no connection, just longtime satisfied customer).
*The RJ45 Y adapters that are currently being sold by Monoprice are crap; Dave Moore says that they used to sell a quality product but changed suppliers last summer or fall. I ultimately had about 40 here and never got more than two or three to work correctly. I found some on eBay which also had bad failure rates, but they were much better than the Monoprice ones (out of 10 that I bought from eBay, about three or four were bad).
I think that if in the future I were wiring an environment that used Cat5 cabling and needed Y connections, I would make them myself from three biscuit jacks.
\dmc