As it happens, yesterday I had to stop a well-performing ad campaign on our site, because the banners were simply too bloated. For a good 10 seconds after the page loaded, their ads would be churning away, loading domain after domain, all to ultimately load a single 160x600px image.

In an attempt to demonstrate the problem to them, I made a list of all the domains that were being loaded by their ad code. Here they are:

  a.rfihub.com
  aa.chango.com
  ad.360yield.com
  adadvisor.net
  ads.ebay.com
  ads.nexage.com
  ads.googleapis.com
  analytics.spongecell.com
  ap.lijit.com
  as.chango.com
  b3.mookie1.com
  bc.ixiaa.com
  bh.contextweb.com
  c1.rfihub.net
  cc.chango.com
  cdn-akamai.mookie1.com
  cdn.spotxchange.com
  cdn.viglink.com
  ce.lijit.com
  choices.truste.com
  ckm-m.xp1.ru4.com
  click.sovrn.com
  clickcdn.sovrn.com
  clients1.google.com
  cm.yieldoptimizer.com
  d.agkn.com
  d.turn.com
  dis.criteo.com
  dm.de.mookie1.com
  dpm.demdex.net
  dsum-sec.casalemedia.com
  dsum.casalemedia.com
  e.nexac.com
  edge.quantserve.com
  ev.ib-ibi.com
  ewr-128.ewr-rtb1.rfihub.com
  fbstatic-a.akamaihd.net
  fei.pro-market.net
  global.ib-ibi.com
  gmtdmp.mookie1.com
  gpush.cogocast.net
  gslbeacon.lijit.com
  i.w55c.net
  ib.mookie1.com
  idsync.rlcdn.com
  image2.pubmatic.com
  js.revsci.net
  load.s3.amazonaws.com
  loadm.exelator.com
  match.adsrvr.org
  msec.xp1.ru4.com
  openx2-match.dotomi.com
  p.rfihub.com
  pix04.revsci.net
  pixel.quantserve.com
  pixel.rubiconproject.com
  pixel.sitescout.com
  r.openx.net
  royale.cdn.spongecell.com
  rs.gwallet.com
  rtb.gumgum.com
  rtd.tubemogul.com
  secure-us.imrworldwide.com
  secure.adnxs.com
  securepubads.g.doubleclick.net
  simage2.pubmatic.com
  soma.smaato.net
  stags.bluekai.com
  su.addthis.com
  sync.adap.tv
  sync.adaptv.advertising.com
  sync.graph.bluecava.com
  sync.search.spotxchange.com
  sync.tidaltv.com
  t.mookie1.com
  t4.liverail.com
  tag.apxlv.com
  tag.cogocast.net
  tag.yieldoptimizer.com
  tags.bluekai.com
  tapestry.tapad.com
  tpc.googlesyndication.com
  uav.tidaltv.com
  ums.adtechus.com
  us-ads.openx.net
  usefb.adsrvr.org
  vap1iad3.lijit.com
  vox-static.liverail.com
  x.bidswitch.net

That's ALL to ultimately load one ad.

And of course, those are only domains; many of those load multiple resources. Basically what they appear to be doing is "waterfalling" through a massive number of third party networks, looking for the most profitable ads. And it works well, if all you care about is revenue. The user experience is pretty terrible though. Even though the ads are asynchronous, so don't block the rest of the page, that amount of crap obviously slows things down in general, especially on mobile browsers. Plus, it just feels bloated when after the page is done loading, it sits there for 10 seconds with the spinner whirling and random ad domains spamming across the status bar.

It's really painful, because this kind of thing works; it outperforms adsense (which is extremely lightweight in comparison) by a significant margin. There's got to be a cost in user retention though, even if your only concern is the bottom line. (Let alone caring about user experience.)