I was constantly refreshing at 12 (shamelessly using the works wifi) and litrally as soon as it hit 5 points it was sold out. 29 attempts and finally got through to be put on the waiting list. Guy said that it was first come first served in terms of tickets that come back but asked how many points I was on. Surely useless information if it is first come first served. Then saw on twitter a tweet from SFA that there were still tickets available at 12:17 (was still trying up to and beyond this). Asked after if there were issues with the system and apparently alot of people had issues.
Long and short of it, if you placed tickets into your basket before 12 then just kept hitting check out eventually it would go through when the system caught up