Telling is lazy and ruins the immersion, so it should be avoided where practical. That being said, rules are meant to be broken, and one of the marks of a good reader is knowing when to break them.
For the "nervous" example, I think it's far better to make the prose make the reader feel how nervous the character is. It may be more verbose, but it'll leave a bigger impact on the reader if you do it properly.
I really like Cormac McCarthy, and he does a fantastic job of using prose to create a feeling in the reader. When there's an intense action scene, words become simpler, sentences sometimes become longer (I've seen sentences span nearly half a page), and the prose moves along faster. When there's reflection/boredom, the opposite happens, with more complex words and sentence structure and generally slower moving prose. He's a master of using prose to convey emotion.
When I read something like this:
> He was nervous. Not the waiting in line to get your picture taken kind of nervous, but the first day at a new school in a new city kind of nervous. He'd been on dozens of dates, why was this one tying his stomach in knots?
I just think the writer was too lazy to paint a picture of the scene and instead expects me to do that for myself. I would much prefer something like this:
> He glances at his watch. 5 minutes to. He motions for another round. Sir, your table is ready. Thanks ma'am. Right this way. He checks the clock by the front door. 3 minutes. Plenty of time. He starts for his napkin, thinks better of it, then adjusts the vase. 2 minutes. He takes a sip, rolling it around with his tongue, and checks his watch. Still two minutes...
Or something like that. I much prefer to experience a story than read about it.