My concern with Alexa is similar to Siri and even the new Voice Remote on the Hopper 2/3.  If your upstream Internet connection sux (U-verse ASDL, anyone?) then you're experience won't be "magical" like the commercials show.  Since I Fold, there are multiple times during the day when I'm uploading megabytes of Folded Protein data to Stanford.  While that's happening, my downstream Internet is severely impacted.  If I happen to ask Siri to do something during that time, I'm likely to get a "Hmmm, I seem to be having trouble accessing the Internet.  Try again later."
And that's before the while "who's listening?" to my Alexa audio stream.  I'm sure Echo uses a VOX technology so it isn't constantly streaming data from an empty house to Amazon, only when there has been a rise in sound levels, but still, I imagine during a party or while watching TV that Echo is sending a constant upload to the Cloud.  That would probably bring my crappy ASDL to its knees.
I did see the v2 Dot is being bundled with many Home Automation devices like Philips Hue Starter Kit or the ecobee 3 thermostat where the Dot is effectively free.  Tempting to try one out, even with all my concerns stated above.