I went to settings, developer options, then selected 'no more than 4 background processes at once,' or whatever it says, I can't remember exactly. That seems to have helped my Bionic perform better. I don't know how many things Android holds onto if you let it decide, but apparently it's a few more than 4.
I'm not rooted, so if you are apprehensive about doing that, give this a try.
I wonder if it's just a lack of RAM with JB, or if it's just the OS? If this phone had 2gigs of RAM, it would be much mo' betta...