I assume that Reginald's complain was not about the data itself, but about the fact that he will now have to move his blog elsewhere - the drag of setting it up, and making sure that everyone can find it.
In fact, it's ironic that Posterous once wooed users by building simple import tools to pull in data from Wordpress (among others). Now, people are using Wordpress's import tools to pull their Posterous blogs back into the WP platform.
If you have your own domain name set up, rather than a free subdomain tied to the blogging platform, there is no issue of worrying about people finding you. Same goes for using RSS if you use Feedburner or have your feed available at a standard location on your own domain.
I have a custom domain name for my Posterous blog, so links to the main site will not break, but links to individual posts will break if the new blogging platform doesn't follow the same link naming convention as Posterous (which most likely they don't)
Do you guys have any ideas/tricks how I can avoid issues like the above, and how to make sure that certain posts which currently rank high in Google search results keep their rank, if possible?
You can do this by dumping the relative paths of your previous blog posts and current ones into your .htaccess file. This won't get all of the old links (category/tag links, for instance) but at least direct links to a specific post will end up in the right place.
Alternatively, is it a good or bad idea to route all traffic to my blog through a VPS I have, so that all the old blog post addresses go to the right place on one of the hosted blog services? (I'm just trying to avoid hosting my own blog, since I assume there are a lot of headaches involved)
With GitHub pages, you don't need to worry about the hosting aspect and you'll always have a copy of your site locally. Pretty sure you can deal with the .htaccess file stuff too.
If you decide to look into this, check out Jekyll-bootstrap too [2].
edit: I've just realised I don't need the code to be merged into jekyll in order to use it (facepalm).
edit2: ok, maybe not as straightforward as I thought. I'm not really a coder so it takes me longer to understand what scripts are doing (and then tweak them so they work for me).
Routing all blog traffic through your VPS is a bad idea, IMHO. Your VPS becomes a single point of failure for your blog - if it stops working all of your posts are unavailable, not just the ones that require 301s.