I have an account set up with them. I'm very pleased!
No minimum, that is correct. There's no 'catch'; they have one brick-and-mortar location, and since there is no building & staff overhead to deal with, they can turn around and give you excellent interest rates.
The only downside is that you have to link an external checking account to them; you can't just open an ING direct account. You transfer funds from your checking account to your savings, and vice versa. It takes about 4 - 7 business days. I wish there was a way to link the ING account BACK to my checking, like an overdraft protection plan, but no bank on the face of the earth allows you to do such a thing (believe me, I've been looking).
Another fabulous online-only banking institution you should check out is
NetBank. You have to deposit $50 to open an account, but they give you %1 interest on your checking account! That may not seem like much, but I don't feel that a bank should hold my money for FREE, you know? Besides, keep $1,000 in there for a week, and get $10 interest back? That's dinner!