Q:

Where's moderator "Bryan Denny"? 

Haven't seen him for a great while.  Is he off for vacation or something else? 

A:

You're right that Bryan isn't very visible on the site lately, but he's still actively moderating.  Don't forget that many moderation actions are invisible to normal users (with less than 10k reputation): deleting posts or comments, removing posts from review queues, messaging or suspending users.  Even the more visible actions (closing questions, editing, commenting on posts that need improvement) are not that noticeable unless you happen to see an affected post. 
The rest of us are probably more noticeable because of the non-moderator things we do on the site: asking and answering questions.  I don't think it's new that Bryan is the least active of us in that sense, but that doesn't mean he's stopped visiting the site or stopped moderating.