I've recommended a lot of people to National Net in the past. No one has ever come and said anything negative about them to me after I sent them over.
BUT.
I've attempted to contact them several times regarding colocation services and never received any response to my inquiries.
The sales email link on these pages is broken too, fyi:
http://natnet.com/colocation.html &
http://natnet.com/contact_us.html
Maybe it's because I'm Canadian :|