Three weeks ago, I swatched for the Ramona Sweater (Ravelry link) from Sensual Knits. I made a nice large swatch, even; then I measured it, washed it, dried it, and measured again.
The yarn I'm using--Elsebeth Lavold Classic AL (50% merino, 50% alpaca, purchased on closeout on a recent trip to Webs) bloomed like crazy when I washed it, and my first gauge swatch suggested I'd be knitting a tent, rather than the sexy sweater Jared had designed so--like a good little knitter--I knit another swatch on smaller needles.
Size 5 needles almost gave me the right gauge, and I was actually happier with the gauge I got, which would make the sweater slightly smaller (the size I knit would have given me 2 inches of positive ease; the photos in the book look like there's less ease that that); my gauge looked like I'd get about half an inch of positive ease--perfect.
The sweater is easy to knit; the pattern is very straightforward. The Classic AL was really nice to work with--soft and squishy. I spit spliced all the way through, so I'd have fewer ends to weave in. Last night I finished most of the seaming (I've left the sleeves unhemmed, in case I want to make them slightly longer):
(Excuse the crap-o self portrait in the mirror that still needs to be cleaned!) A little bit on the negative-ease side, there. Too much so. Which is where the trust comes in: the yarn bloomed in the swatch and I'm trusting that it will behave the same way in the sweater. This project's gone so well, though, that I'm a little nervous about the next trying on!
And now it's had a bath (four, actually, since there was some excess dye in the yarn) and is blocking to--hopefully--the planned-upon size. Not quite an FO, since I still have to hem the sleeves and snip some ends (they're mostly woven in, just not cut), but pretty darn close.
So keep your fingers crossed that the swatch didn't lie (or at least didn't lie too much)!