So let's say I have 2 sites- one for widgets and one for doodads. We all know that widgets and doodads have nothing to do with each other (which is why there are 2 different sites instead of one).

On my widgets site, I'm getting ads for Worldwide Doodads. I definitely don't want them on my widgets site, so want to add their URL to my competitive filter (now that I have an extra 300 spots to fill- thanks Google!). But I would love to have them on my doodads site, so I don't want to add their URL to my competitive filter list for that reason.

Google- what's a poor webmaster to do?! Yes, I could get another account to use just on the doodads site, but you tell me not to do that. And what about my sites for doohickeys, thingamabobs, foobars, gizmos, knickknacks, whatchamacallits, and examples? I'd run out of e-mail address to use soon. Plus it might look (to Google) like I'm trying to do something nefarious.

Of course, the bigger question is why are Worldwide Doodads ads showing on the widgets site in the first place when they have nothing to do with each other. Well, one section talks about using widgets in Elbonia. And you can also use doodads in Elbonia, so Google has decided it's an appropriate ad!