What is the etiquette around blogging about conference talks?
My general rule of thumb in these matters is the following. If you don't want to communicate your results yet, you should not be talking about them in a public seminar. Or, at the very least, you should put out a disclaimer initially that you will be discussing confidential material (I have seen some company talks that started with a similar disclaimer, but probably more for legal reasons than because the presenter themselves cared deeply about it). Barring such a disclaimer, I think it's a fair default assumption that the presenter does not mind their thoughts spreading.

Another safety line you can take is, after you published your blog, making the speaker aware of it. I have found that Twitter works very well and non-intrusively to that extend:


  .@coolprof summarizes topic X, feels more research is needed on Y. Summary: http://my.blog.edu


In that case you can assume that if the speaker really does not want your summary, or parts of it, on the Web, they will tell you.