I personally like the incase sleeves. They're simple and cheap and does the job! No need to spend $100+ on premium leather and wool, because that's going to help my protect my MacBook how??
I decided to get one yesterday from BB for $39.95, hoping that within the 30 day return/exchange policy incase will come out with a sleeve specific for the rMBP. The one below fits, but it's got a bit of slack. I needed one now, I've been paranoid since last week.
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ehh, my thumb looks weird.
I personally have to second this opinion. My old incase has lasted 5 years (through college mind you, so frequent wear and tear), and only this month have I seen fraying.