Mostly irrelevant, but:
You cannot flank with a ranged weapon... though there may be some obscure ways to get around this, such as the "Master of the Order of the Bow" epic prestige class. Ranged sneak attacks are all about finding a way to negate dex bonus, such as by being invisible. Skirmish is easier from range, though it has its own host of limitations, and also does less damage.
The cool thing about this feat is that it takes anotherwise suboptimal choice (crossbow v longbow) and makes it appealing to some characters. Pretty feat intensive though... between this, weapon focus, and rapid reload (not a prerequsite, but an essential feat if you're concentrating on crossbow) you had better be serious about your dedication to the particular weapon!