I do it, for sites that particularly concern me. For example, it's been... interesting, to watch the ongoing changes in Google's cert chains. And when, many months ago, I commented on these, I received a number of silent (no comment) upvotes.

If you're not looking at the whole chain, you're ripe for MITM, particularly with the cruft in default root certificate distributions as well as ongoing changes in entity alliances -- whether free or coerced.