Good question, but I've never heard any complaints such as that about those single cup brewers. I have tried coffee and hot chocolate from a Keurig and both left ALOT to be desired in the way of authentic taste. They're OK for a decent cup with repeatability, but that's where I'd draw the line.
We have one - I actually won it on Twitter for posting the most tweets about coffee on a single day! My daughter likes hot chocolate and my son makes coffee once in a while. No flavor transfer, but do change the water every day or it goes yucky!
