Google Currents has been notorious for causing sluggishness. If you don't use it (it's a news aggregating app), go to Settings/Apps/All, select Google Currents, and disable it.
If you do use Currents, open the app, go to its settings, and turn off the background sync.
Also, have you tried powering the device off, and then turning it back on again? If there's some rogue app that's causing problems, this will typically stop it. There are other advanced techniques and apps that can help, but these are simple things to try.