I dns poisoning is something to be concerned about. My college's dns servers were compromised this time last year and I was the one who detected it. I even let the tech's know about the issue and they did nothing for a few days. Hotmail.com was the largest site affected.
I have already emailed buzz twice today to that has to live in the forums.
The likelihood of a DNS server being compromised by a Denial of Service attack is very low.
At VeriSign, the more or less are always fighting off some kind of attack as they get many everyday.
I talked to a tech at my dad's co and he believs that it would be very difficult for what was described in the cast to happen.
As for it being worrying, a few days ago I had this discussion at school and it did not really worry us (we were plotting to borrow the google domain for a while as a tribute to a leaving teacher - you know, as you do!)