Yeah it's tacky, which is why you should avoid doing it if face to face is available, but I wouldn't give too much of a fuck over whether it's "cool" or not.
At the same merit, however, it really shouldn't matter to either of you how the asking-of-out happens. Saying stuff like "If he doesn't ask me out face to face he's clearly not serious enough for me!" would actually put me off asking someone out at all, by text, facebook or otherwise...If you've got a five year plan before a single date has been had, IMO, you need to slow the fuck down and chill the fuck out.