The only issue I have with KVM/IP switches is because of the additional cables needed. I'm very much a fan of keeping things simple and we more or less strictly use ILO's, LOM's, or whatever the flavour is according to the manufacturer.
I'm especially not a fan of Avocent. We used to use their CPS and DSR switches which is extremely old and out of support now, but I've seen some of their newer systems that aren't too far off from those. It requires entirely too much work and resources to want to network a large scale data center.
I have a different experience with Avocent equipment. Their equipment is cumbersome, requires additional setup that is unecessary, and the application end is poor in performance and generally not robust in features (unless you want to spend the mega bucks and get all the bells and whistles).