Now, if only they could talk Zifty (Zifty.com) into merging, Atlanta would have every restaurant available in one service.
The latter seems nice if I already have a restaurant in mind, but if I'm too lazy to cook on monday night, I'm not going to go through the apps one-by-one.
1) Standardized ordering API allows restaurants with "their own" ordering system to be listed on GrubHub/Seamless.
2) One company (probably Grubless) serves as an aggregator but also sells a lame iframe-for-your-website/custom-app combo.
Restaurants should probably hope for #1.