Maybe it's been discussed elsewhere, but haven't seen it reported that for Gmail notifications to vibrate on my S2, I have to have vibrate turned on in notifications for Gmail on my phone. This isn't optional cause I don't like my phone to vibrate for any notifications. Just thought I'd share in case anyone is perplexed about why their S2 doesn't vibrate for Gmail. Check your Gmail phone settings. Oh, and I'm using a Nexus 5.