Its always killed me that in D&D every race can and will interbreed with every other, without any consideration to a reasonable persons ability to suspend disbelief. A half-elf I can grasp, an Owlbear... I don't think so.
And don't even get me started on the following, the logistics of copulation just make my head hurt.
half dragons
half elementals
half ooze
insectile
half giant
Now I know many people will want to fall back on the "its magic" arguement, and to them I say: whatever gets you through the night. But frankly I think it is high time that these creatures be reclassified to what they really are Aberations (and of course take the appropriate reduction in BAB, saves, etc). I also believe it is high time for a new prestige class be developed, the Morality Police: Beastiality division.
As for a Drow/High Elf, I recomend a nice full-body zebra stripe tattoo.