I wouldn't consider myself a network engineer, nor do I have any formal training, but why don't ISPs peer with every other ISP? It would only save EVERYONE money if they did this, no? Only issue I see is with possibly hijacked / malicious AS owners, but that's not very common to do without being caught.
Some ISPs have very friendly peering policies, but some obstacles facing even the friendliest ISPs are: *Poor operator reputation or significantly different networking mindsets may make some peers undesirable *Potential peer is attempting to become a tier-1 and demands paid-peering *Potential peers do not have similar POPs or budget for transport between POPs for peering *Some ISPs do not have the ability to easily determine the destination of their traffic and which peers would be most advantageous in terms of transit reduction *Potential peer is lazy or reluctant to make changes I'm sure I'm missing a few, but I believe these are a couple significant obstacles to a more 'meshy' internet. Nathan