The plugin work greats and provides loads of features that most novice users would enjoy having on their blog (although there are plenty of plugins that will accomplish the same things). In addition, the stats feature is quite amazing.
My one (huge) problem with Jetpack? It requires a connection to WordPress.com. While this does not really bother me with things like Stats, it renders other things (like subscriptions) useless for those that want to keep users on the main blog.
Once Jetpack implements the option to use not WordPress.com for other things, I will give it a better rating.