I did a quick search of the forums but didn't find anything related to this. I came across this page on the FCC's site that states deauth attacks and jamming of WiFi are illegal in the US as of January, 2015. They also state the following:

In addition, we reiterate that Federal law prohibits the operation, marketing, or sale of any type of jamming equipment, including devices that interfere with Wi-Fi, cellular, or public safety communications. Detailed information about the prohibition against jamming is available on the Commission’s website at http://www.fcc.gov/encyclopedia/jammer-enforcement.

If you read the example they gave about a Marriott hotel deauthenticating users it appears the FCC doesn't know the different between that and jamming a signal. Of course they added that catch-all statement that any device that interferes with WiFi communications is illegal. Page 2 of that document states that no commercial establishment is allowed to block WiFi communication but the next paragraph down has the quote I posted above. It would appear that using the deauth feature of the Pineapple is now illegal, unless if I'm misinterpreting this.