I bought a set of these sheets 3 years ago and another set this winter - I absolutely love them.
They are good for both winter and summer - unlike Percale, they aren't cool when you first get into bed so they're great for winter, yet they aren't too warm feeling for summertime use. Unlike flannel, they don't pill, so I found them to be a great all-year sheet.
Yes they do have wrinkles as noted in other reviews but I just keep fluffing them out and pulling them tight around the mattress when I make the bed.
I have tried very expensive sheets of sateen, percale, egyptian cotton, portuguese flannel and others and have yet to find a sheet as good as this one for all-around use. My 3-year old sheets have not pilled and the new ones I bought are just as good - unless the wrinkling in the bed is an issue, I highly recommend this product.