I just put in a new Avaya VOIP system, and ~30 of their (Nortel) Enterprise Ethernet switches since last Christmas. Good to know we've dodged the bullet of being owned by Evil Empire #2.
Avaya gear is OK, but as others have said, it is a bit pricey, and seems to be a bit "trailing edge" as far as features. You can definitely feel the ghosts of a Great Ancient Telecom provider when you are dealing with them. Everything is very regimented and flexibility is, ehh, what's flexibility?
Their customer service completely sucks donkey balls, though. If a switch goes out, you can't call and talk directly to a rep, you have to fill out a web form (after you remember/reset your login info) and wait for them to call you back. That happened last week when a POE module went poof in one of their switches. I was not happy about that, and told them that for what I paid for these switches, I shouldn't have to deal with no stinking web form. That got me a "click" from the other end. Great. I shoulda bought HP Procurves.