I buy it when I need both sorc boots and tenacity. Seeing as moonflair spellblade gives you about 60 ap and tenacity while the alternative to sorc boots gives only 400 hp, 30 ap and the 20 spell pen. Its a solid buy. So is Cloak and Dagger for AD champs who need tenacity.
icyneesan said: Who the hell buys Moonflair Spellblade?
Several reasons, mostly situation-dependent. For one, it could be the same reason why LeBlanc would love to have Haunting Guise: it's a great item that fills a good niche, and can be sold later on in lieu of better/more appropriate items. Another reason is for Dominion or for quick, cheap but effective gameplay needs. Or as was already stated, it may be a good item if one desires Tenacity on Ahri but wants the magic pen of Sorceror's Shoes.
Back on topic, I just found my new wallpaper. Hot DAMN.