Sucks I know but it was perhaps to be expected that sheer weight of numbers would be an issue. I got back on no problem then half an hour later PSN disappeared for an hour sith no warning... and since then it's been back.
Reminds me of when Half Life 2 launched and Steam just couldn't handle the sheer weight of numbers.
It'll settle down as more and more people change their password and volume settles back down.
My main gripe is it would have been so easy - and obvious - for Sony to advise about potentially slow service initial due to demand or the potential for delays receiving emails.
Always warn and apologise in advance and customers will be more understanding I find.