Josephwrote a review of DAKINE Concourse Double Ski Bag on December 21, 2011
Although I haven't yet flown with this bag and I cannot speak for its long-term durability, it seems to be very well constructed and it has more than enough space for skis, poles, boots, etc. I probably won't check my boots in the bag, but it is nice to know I could if I had to.
In general I would suggest you follow Dakine's sizing guidelines, but in certain situations you may be able to get a longer ski into a smaller bag. Especially with twin-tips and extra large front shovels on many modern skis. I can easily fit a pair of 190cm Volkl Katanas in the 185cm bag.
Although many people may use the extra space, I wouldn't mind having the same bag and protection in a slightly tighter package.