i've listened to 3 WTFs so far after i saw it was recommended here. I started with the dave attell episode, which i thought was a great interview (sidenote: i also think attell is great whenever he's on howard stern, too, so i could be kinda biased). then i tried out the brendon small episode, which was boarderline unlistenable. i was hoping to hear more about "home movies" and that show i can't spell properly, but most of the conversation (i bailed; didn't listen to the whole thing) was marc interrupting brendon every time he was about to answer marc's question, and then marc talking about how he plays guitar, but isn't very good. it was really frustrating to listen to. i listened to about half of the h. jon benjamin episode today and i enjoyed what i heard.
i'll try it again for some other guests i find interesting, but overall i wasn't blown away or anything. and, i dunno, i can't really see marc fitting in on TBS.