Cogent has been great for us.
I see a lot of negativity here regarding Cogent. I am the network operator of an ISP in San Martin, CA. Our primary link is a 100Mb Cogent link. Our secondary upstream is a 10Mb (Burstable to 100Mb) link from Charter. We made the switch to Cogent from XO; going from an XO OC-3 to the Cogent link.
The link has been great since it was turned up. We had some minor (~1%) packet loss a couple months back, but after speaking with their support staff (who are actually pretty knowledegable), we had the packet loss taken care of. (Turns out the problem was not with Cogent, but with the owner of the fiber.... AT&T ).
We did have quite a few customers call in today; both customers who could not access anything on Sprint's side, and vice-versa. We have routed that Sprint traffic over our secondary connection, and all is well.
I'm not saying that Cogent is "all-that", and I am not saying that those who have been slighted by Cogent in the past are wrong or full of it, but I just wanted to give an example from the other side of the spectrum, that sure, they do offer "Mc-Bandwidth" at very low prices, but our mileage so far has been stellar.
I don't know all of the facts regarding the whole Cogent / Sprint-Nextel soap opera, so I can't really take sides or point the finger.