I've been with them for about a decade. In that time I've only ever had one negative experience and one moderately annoying experience.
The negative experience was when we were exactly 10 cents short and one of their accountants got a little aggressive on the collection. We paid it up, but he was nothing less than ridiculous with how emphatic he was about the whole thing. We're documented referrers, having referred about a dozen people, so while we'd never ask for more than what we're entitled to, a break until the next month seemed reasonable.
I was recently annoyed when I needed to get a password reset for a friend (And one of those named referrals). 45 minutes on hold is a surreal experience.
Otherwise, they're an amazing ISP. They consistently fight federally for better deals, and they're known for passing those deals on to customers. Last year they had a reduction applied to everybody's bills. I own the VDSL Modem I connect with, just as I bought and used my own ADSL modem in the past - no rental fee! I also have unlimited bandwidth.
For me, Teksavvy has been a fantastic deal. Just write your passwords down.