It seems very sensible to me. Tieflings appear in most of the standard settings, these days, particularly in the Forgotten Realms, which seems to have become host of most of Planescape's exiled races (Tieflings, Aasimar, Genasi etc.), and they're basically an appealling concept.
Claim that they're "from anime", or "from computer games" is utterly moronic. People have been having part-demon characters in their games since 1E. Jeez, people used to talk about "cambion characters" all the bloody time (usually in stories of munchkindom, admittedly).
Not only that, but they're drawn from myth and history much more than BLOODY HALFLINGS, for god's sake. If halflings were hobbits wtsnfo I'd cut them a break, but as of 3E they seem to be pointless short people who don't have the stones to be either hobbits or kender, or even say, "trolls" a la Tad Williams' Memory, Sorrow and Thorn.
Now, I have to admit the whole "giant horns and a three-foot lizard tail!" deal is a bit of a shocker, but presumably that's just the iconic Tieflings, and actual Tieflings will be more varied. I sure as hell hope so. Of course, if they're not, people will just house-rule it, and by 2010, there will be a Tiefling sourcebook with alternate heritages and what other feats/class specials they grant, no doubt.
Then again, I love half-races, I always have. It's an appealling concept to me, and it's in blimmin' Lord of the bloody Rings, so I don't know where people are getting off implying it's newfangled or something. It's old-skool.