Me thinks the OP is trying to spread FUD.
I've made many many transactions with Coinbase both ways and it's been always a great experience.
If there's any issue, it's with the OP's financial institution. Probably changed the terms of service or something.
GOX, GTFOH. Not if Marc Andreesen has anything to say about it. If you've never heard of him, you should.
FUD, because it works for you it must all be fine for everyone? Coinbase will not provide details regarding why a transaction was cancelled, just that it was high risk. When the market is swinging in a direction that isn't conducive to completing the sale I have seen my transactions canceled, in some cases many times in a row over the course of a week or two. I have also have successful 5K plus transactions with them.
In any case since Coinbase will not share the details regarding why a transaction was cancelled the OP is asking a legitimate question. In my case I took my business to Bitstamp and haven't been happier, Coinbase lost my business due to their lack of transparency but obviously they are working fine for some people..
OP tried to compare Coinbase to Mt. Gox, if that's not spreading FUD, I don't know what FUD is.
Last I checked Coinbase had over 1 million wallets, added top personnel from Facebook and Amazon to their staff, and backed by Andreesen Horowitz.
I think unfortunate cases like you and the OP experienced are extremely rare not the norm for Coinbase. Without any proof from the OP, it smells more fishy than anything. Why is he posting this on a board read by thousands on a daily instead of rectifying his situation?
If anything, they're one of the bright beacons of Bitcoin business. They make transfers and payments really easy. Like NOOB easy.