It's worth noting that both of these issues are not specific to Jetpack: you would receive the same results if you were to replace Jetpack by other plugins offering the same features.
Parallelize downloads across hostnames
Older browsers cannot allow many concurrent connections for a similar hostname; as a result, if your browser has to load many different files from the same hostname (domain), not all resources will be downloaded at the same time. That's less and less problematic as people switch to newer browsers, but Pingdom will return such results as long as your site includes different resources from the same domain.
You could work around this notice by using the Minify engine included in the W3 Total Cache plugin. Most of these resources would then be grouped into a single file.
You could also use the Jetpack sharing advanced options, disable Jetpack's CSS and JS files under Settings > Sharing in your dashboard, and load your own, bundled resources instead.
Serve static content from a cookieless domain
You can work around this notice by using a CDN to serve some the static files on your site. There are many CDN services out there, and I don't use any on my sites so I wouldn't be able to recommend one over another, but I'm sure you could find some useful advice here in the support forums.
You can remove some of the files listed here with Jetpack sharing advanced options, as I mentioned earlier.
Personally, I don't think these notices are that important as long as you don't see a bad effect on your site's performance. You could make a few tests, do a few speed benchmarks with Jetpack, with Jetpack and a caching plugin, and then with other plugins offering features similar to Jepack's ones, and see what's best for your site.