An example would be in order, and, right off the top of the list, I would have to say the best use I've seen in recent gaming would be in Red Dead Redemption. It actually makes sparing use of cutscenes, choosing instead to use travel time to relay information and what scenes there are end up being more memorable and interesting. This is contrast to COD: Black Ops which chose to use almost no cutscenes and attempted to deliver all its information through the course of events, it just doesn't give the player enough engagement to get involved. Mafia II struggled a bit with this balance, the scenes were a bit long at times, even though they told a great story, and they might have killed the game if it hadn't been for the fact they were skippable (I found this particularly true with the expansions).
This is the cardinal rule that gets broken all too often, and one you'll hear players complain about above all others, when cutscenes cannot be skipped over. Put as little or as much s you want in there and let the player choose how they want to treat it, especially if you're trying to sell replay value.
A bad example? The worst I've ever seen is in a game called Bonetown, an X-rated game about sex and drug use, nothing innovative or compelling (beyond the nudity), but largely playable; that is to say largely playable other than the frequent, unskippable, and boring custcenes. They're meant to be funny and entertaining, but the game is just difficult enough that you often end up sitting through the pedantic dialog over and over again, waiting to see if you'll get it this time. I guess people who write porn aren't really cut out for interactive creativity, who'd have thought?
Pay attention to the next game you play and judge for yourself, if you don't enjoy it due to boredom or difficulty, there's at least an even money chance this is due to the data being relayed to you as a player, a well made cutscene might engage you more or help you out of a bad spot. If you are enjoying it, it's very likely due to well placed cutscenes, providing engagement and information that makes you want to stick around.