As far as the security algorithm itself is concerned, a very long, random PSK is extremely secure.

However, there are human factor issues that come into play: that long PSK has to be written down somewhere and that location must be kept secure; the number of people who have access to the key must be limited and all of them must carefully maintain the security of the key; if the key is compromised you must manually change the keys on all clients; etc.

Another issue is that with a PSK you have no way to map a given wireless connection to any individual user, as you would with 802.1X. So if an EAP account is compromised you at least know who to yell at, whereas if your key is compromised you have no clue.

Nobody's going to crack a 63-character passphrase using over-the-air tools. But they won't bother. They'll just find a way to get into your helpdesk office and take a picture of the whiteboard where it's written down.