Eyesore Advertising

How much of an eyesore would a small advertisment be at the top and bottom of the screen, while the player was going some out of character things (IE anytime the player doesn't see the 3D landscape, regardless of whether there action is apart of the game - posting something on an ingame board, or maybe more involving - or not - changing the settings)? I ask this in the game idea section because a game I'm designing needs a semi-persistence, but nothing on the scope of EQ, AC or UO, so one or two central servers would have to be maintained, and I need to finance them. I know battle.net has advertisements in the chat screen, BUT my game will probably not have this area or capability.