They're not kidding: the trail goes up and down like a yoyo and it can be quite slippery when it's wet. (And you want to go when it's wet, as the waterfalls are better when there's plenty of rainwater running off the mountain.)
Bay Area Hiker thinks it's 4.2 miles but notes that the claimed mileage varies; the California Hiking book says 6.5 miles. It certainly felt more like 6 than 4 to me. Mind you, California Hiking also suggests 2.5 hours: we did it in closer to 4 hours, starting at 1:30pm and walking off the mountain at dusk at 5:20pm.
Fantastic views of the canyon and over Clayton; and it's nice walking alongside the creek and the falls as you're never far from the sound of water. The falls are unspectacular by Yosemite standards, but there aren't really that many waterfalls in Northern California so you take what you get.
I was struck by one species of tree, common in a couple of areas which looked like regrowth after fire: fairly scrubby, waxy green leaves, and very smooth shiny orange bark. I liked to think of them as Fake Plastic Trees, but I'll try and look 'em up at the library and find out what they really are.
[Update: they're manzanitas, a California native. The botanical description and photo doesn't really do justice to the young trees I saw, which had very vivid glossy bark. The photograph here isn't up to much either, but the description is pretty close to what I saw.]