It seemed that way for me and for others who got it earlier this week. Today I turned off Google Now and ran my phone in safe mode for a couple of hours. I then rebooted to normal, kept Google Now off, and things are a lot smoother than they have been compared to the prior 36 hours. Still not sure about the battery, because of the update I haven't had a "normal" usage day since ICS. Tomorrow morning will be the test; for the past two days Gmail has frozen in the morning as I'm flipping through emails that came in overnight.
Bottom line: if you're unhappy with lag and stuttering in JB, try turning off Google Now. Still can't get Light Flow to work for Gmail, though, and turning off Google Now will probably not solve any third party app issues. But it does make things feel better, at least for me.