Cameos just aren't what they used to be. When an awesome celebrity finds his or her way on to one of your favorite shows, it seems really exciting. For a second, you're tricked into being super star struck. Whoa, that's Jack Black on 30 Rock! And then you stop and think, wait a second, that's also Tina Fey, Alec Baldwin, and Tracy Morgan on 30 Rock. Hmmm, suddenly Jack Black doesn't seem all that exciting.
The impact used to be much stronger. Naturally, we'll start with an example from Saved by the Bell: The College Years. There's an episode when Brian Austin Green makes a cameo (as himself) at the gang's Thanksgiving dinner. I'm sorry, but how did Saved by the Bell: The College Years get one of the most popular heartthrobs of the time to come on to one of the eighteen total episodes it ever had? I guess it didn't help the ratings all that much in the end. On one episode of Full House, Frankie Valli (no Four Seasons) makes a cameo and serenades DJ on behalf of Nelson who wants to win her back. FRANKIE VALLI?! That's awesome. I'm sorry, but cameos need to get back to their roots.
I guess shows are too good now, so the cameos can't really add much excitement. For a concluding example, check out the horrendous acting of Julie from Friday Night Lights in her appearance on 90210. I guess talent in one teen soap doesn't mean talent in anything else (Katie Holmes, anyone?)