Poll 1,000 users and 10% of them will say they want to write a blog.
Give that 10% a blog, get everything set up, and come back in 6 months. maybe 10 users will have written more than a "Hello" post or a few banal anecdotes about their cat.
It turns out that most users who think they need a blog are better off actively participating in a "Coffee House" type forum. There is really little difference in sharing their life experience between that and a blog. The traits that make one a successful forum poster don't necessarily translate to the skills required to be a quality content author.
There's no doubt that Wordpress is the best-of-breed blog software. XenForo could spend 2 years trying to copy it but why? WP is dead easy to install, it's in active development, and there are bridges to forum software to display recent posts, or include blog posts in the forum somewhere. I wouldn't even mess with trying to integrate user databases. Just sign up those 5-10 of your users who will actually show an interest in posting articles with blog accounts and treat them as a team of authors helping to build your website.
It's been stated that XF is going to focus on being a quality forum, and allowing developers to write add-ons and plugins. I'm not Kier, but it seems rather unlikely that XF would add a shopping cart feature to XF beyond the rudimentary paid subscription system. I just think it's totally beyond the scope of XenForo to deal with tax laws, shipping calculations, inventory management, order tracking, and all the other cruft that a shopping cart requires.
If you are running a sales site that needs forum support, I'd see if you can get someone to modify your shopping cart software to automatically create an account in your XenForo forum, populate the user account with the relevant information, and then e-mail the user information on how to login to and use the forum should they be interested in using it. Most purchasers of products don't feel the need to comment on it unless there's a problem.
