My WP blog was running unusually slow after installing this. I ran a number of speed tests, and determined that Jetpack was slowing me down by an absurd amount -- even without Photon enabled. After disabling Jetpack and clearing cookies, I got a 3-10 second increase in speed. Ridiculous!d
I like the jetpack features, but the slow speed makes it unusable.
I use WP 3.5.1 and the Clean Retina theme. Got an additional speed-boost using the W3 Total Cache plugin and a free Cloud Flare account. Now my pages are blazing fast. WTF Jetpack?