I know that this is a relative question and a different answer may apply to different site styles but I'll try and be descriptive in this example.
Current: Displaying a table where each row has an image floated right and text beside it. Each row has a 1px black border around it and the table is 540 pixels wide, the images 100 pixels of that.
Proposed: I'd like to squeeze the existing content to cover only 420 pixels and to place a 120x600 adsense unit to the right of that. The unit would also have a border around it and be distinct from the other content but still right next to it.
The effect - some images may occasionally align with the ads but there is a border between them. I'm trying to give adsense a shot at some high value content, as per their heat map, but is having less than 5 pixels between image and text too close even with a border?