This is a review of wordpress.com integration in general, of which Jetpack is only one part.
I suppose jetpack is a great start, but there needs to be a bit more work, probably on wordpress.com itself, before better integration will happen. WordPress.com will recognize your self-hosted blog as your 'primary' blog, and now finally things like the wordpress plugin for Chrome will recognize that setting, but still we self-hosted users lack the ability to use the 'reblog' function as easily as our .com cousins can. (*cough* tumblr! *cough* *cough* pardon me...)
Another thing about Jetpack that might make it more attractive would be if every single one of its features were optional and/or more clearly able to be turned off. I'm sure my server host doesn't like it when I'm running all kinds of built-in stuff that I can't turn off, when all I really want is one or two parts of it.
In summary, Jetpack is a good idea, but it needs work.