d-air is for chain-throwing floaties like peachRagnarok91 said:-IC's dair and uair are bad, cept I think you can use them for desynch grab combos
u-air juggles fast fallers at high percents and floaties art low percents
both have disjointed hitboxes and are thus sexy =)
peach's u-tilt has uses, but it's never the best choice by any means. it just looks funny, that's all.