The added features of this plugin do not justify the performance penalties this plugin introduces to WordPress sites. On my installation, enabling JetPack with just the stats enabled caused a major increase in page load times. Using the P3 plugin from GoDaddy, I could pin it down to Jetpack:
P3 (Plugin Performance Profiler) - 0.0024 sec - 1.26%
Akismet - 0.0021 sec - 1.11%
Gpp About You Widget - 0.0009 sec - 0.45%
Gpp Base Hook Widgets - 0.0019 sec - 0.99%
Gpp Slideshow - 0.0157 sec - 8.14%
Gpp Testimonials Widget - 0.0007 sec - 0.36%
Gpp Welcome Message - 0.0111 sec - 5.76%
Jetpack by WordPress.com - 0.1318 sec - 68.53%
Reveal IDs - 0.0052 sec - 2.72%
Social - 0.0056 sec - 2.93%
Twitter Tools - 0.0149 sec - 7.75%
With Jetpack enabled, the impact of plugins to load time was 48.77%. Once I disabled Jetpack, that value went down to something like <2%.
Jetpack is garbage and the name itself is bitter irony when you look at the performance impact of using it.