We have a site offering a voip app in 4 languages. Users are currently 302 redirected from the root page to /language subpages, depending on their browser language.

Discussions about the sense of this aside: Is it correct to use a 302 redirect here or should users be 301 redirected to their respective languages? I don't find any guideline on this whatsoever...

No use in having a blank robots.txt. Minimum requirement if you want to have your site crawled is this:

User-agent: *
Allow: /

Note that Gagans example above will block the entire site.

Maybe linking each blog post might be overdoing it. But link to your sales pages where it makes sense, i.e. where you specifically talk about the products/services you sell. Don't overoptimize your anchor text though. But smart internal linking can indeed improve authority of your linked-to pages.

100 points for you Martijn, thanks! I'm pretty sure you've found the problem and I'll go about fixing it. Gotta get used to having https used more frequently now...