Maybe it's the recession, but I'm noticing more and more recognizable stars in bit parts on television lately. These aren't huge stars by any means, and for the most part they are people who've mostly made their career in television to one extent or another. They are, however, a step above the usual nameless extra that might have filled the role in days gone by. There are two cause and effect type things related to this phenomena, at least in my household.
The first is the "where do I know this person from" question. My computer is not in the same room as my television, so while I can and do eventually go look up the answer to this question, while I'm watching I am left to scratch my head. This can be quite frustrating, especially when I can almost see a person in the last - or most famous - role I've seen them in. More often than not, the answer kicks in before the show is over, but not always.
The second is more detrimental to my viewing pleasure. It happens when not only do I recognize the person, but realize that the brief two lines they just spoke to the detective (or whomever) was surely not enough to justify the paycheck they picked up for the episode. Which means they're going to figure much more prominently into the plot at some point. They aren't always guaranteed to be the killer - unless it's Law and Order - but watching the show you just know you haven't seen the last of them.
Which kind of takes some of the suspense and intrigue out of things. Granted, you could argue that instead of the "is this person the one" it becomes "ok, how will they fit into this" but I much prefer the first question over the second one. I have yet to see any show take this and exploit it by making the actor in question a red herring, where as the viewer I sit there and think "they're going to be important" and then they aren't. I suspect that's more a question of "we paid for so-and-so which means we need to get our money's worth" than it is a failing on the part of the scriptwriters.
In fact, given that the script is written long before the actors are chosen, that's pretty much a given. So perhaps the fault lies with the individual directors for the various episodes. Or as I said in the beginning, with the recession that leads these people with more famous faces to find work where they can.