I made a rookie mistake with this pattern: substituted worsted weight yarn for the DK called for by the pattern. But there was a reason behind my goof-up. I had been working on other Fair Isle hats and they were turning out too snug, so OF COURSE casting on 136 stitches did not raise any red flags.
Pattern: Plaid and Diamond Fair Isle Beanie, by Martin Storey
Yarn: Cascade 220 Superwash, in colorways 854 (navy), 816 (gray), 253 (desert sun)
Modifications: used worsted weight yarn instead of DK; knit in the round instead of flat
After blocking, the hat became YUUUGE. Not wanting to waste an otherwise perfectly good hat, I resoaked it and threw it in the dryer with the rest of my laundry. It is still a bit loose, but bound to fit somebody with a big head.
I haven't done much colorwork, and due to the fit problem I was experiencing, I turned to this tutorial on KnitPicks. Not only does their technique anchor floats, it evens out the knitting. I highly recommend it.