I've flown a couple times with my inline skates, though not recently. The flights in question were on NW, say 2002-2003-ish, I think. Round tripped DTW <-> DEN, then another trip DTW <-> SIN. Both times, if I recall, I flew outbound with my skate bag as a carry-on and then checked it on return. Noone batted an eye, but, again, this was ages ago.

I have a skate bag like this:

(Hmm, turns out I can't post URLs yet. Search "transpack expo skate bag".)

In general, it functions well enough as a skate bag in that it sensibly stores the intended items (skate, helmets, pads), but it is a bit awkward and unbalanced. It served its purpose OK as a carry-on, but it is definitely a gear-specific kind of solution, and I certainly wouldn't recommend it as a more general purpose bag.

I don't skate any more (discouraged by doctors due to ankle injury), but if I were to fly with skates again, I'd use my existing bag or get something like this:

(Search "transpack sidekick pro".)

I like the looks of that style better. (Though I shouldn't skate any more, I can still snowboard.) There's another style of bag I've seen that also hangs the skates/boots on the exterior, but places them more centered on the back and not out to the sides.

In short, there are a couple skate/boot specific solutions out there.