I just came across a blog which is running adbrite banner along with adsense banners, is this allowed?
you can use other ads as long as they are not mimic with ad sense ads . Adbrite ads are not totally contextual and have little different ad formats . so it is allowed . But using adbrite ads for low traffic sites is bad idea which greatly decreases CTR thus ad sense earning . But for site having high traffic can get banners paying higher like $25 per day etc .
Yes, I have even emailed google on this issue and they stated that it is perfectly OK to use them together as long as adbrite ads cannot be mistaken for adsense ads. I would suggest only using adbrite if you have a high traffic site with over 2k visitors a day. Otherwise, it seems to be a waste of time....