I absolutely <3 Ad Injection, but there's a feature I'd like to request that would make it even better -- configurable start offset & configurable gap/frequency.
For example, let's say on the front page I have 10 posts displayed. Right now, regardless of what mix of top/random/bottom ads I use, it will display an ad for the first post (unless otherwise restricted/excluded by category/tag/author/length), and continue to display ads for each subsequent post until the limit is reached. With the plugin in its current form, if we have e.g. 2 random ads set, they'll of course display on the 1st and 2nd post bunched-up one after the other, leaving the remaining 8 bare/ad-less. Visually, this is kind of yech, and looks weighted on those first two.
What would be great is to have the option of a start offset, which would allow setting the first ad to be displayed on the 2nd, or 3rd, etc. post rather than the first (and not have to rely on cat/tag/auth methods of exclusion). In addition to this offset, it would also be handy to be able to set a user-defined gap between posts, so that instead of ads being displayed on the next sibling post, you could set it to skip 1 or 2 or 3 etc. posts, and then display the next ad. So in my front page of 10 posts with 2 random ads per page, I offset the start by 1, so the first ad displays on the 2nd post, and then configure the gap between to 3 so it skips the 3rd, 4th, and 5th post, and thus displays the second random ad on the 6th post. That way, it would have a nice clean ad-less first post, and some breathing room between the ad on the 2nd post and the one on the 6th.
It would of course require some sanity-checking of the posts per-page value and adjust the offset and gap accordingly, but this feature would add a great deal of flexibility in terms of display/visual dispersal and not force it to be "bunchy" like it is now, and also reduce the amount of "ad blindness".