What do you think a good target is for CPU Utilization on an ESXi host?
I admit that it was tempting to throw out a number to answer the question. But I realized that I had just been given a great opportunity to educate someone on some vSphere design considerations. And you'll be happy to learn that at no time did I ever utter those ill-fated words: IT DEPENDS. (Even though in this case, it really does.)
Instead of blurting out a target, I explained that we needed to establish some facts about the vSphere environment. Do they have a cluster? Seems like a stupid question, but you'd be surprised how many sites I visit with plenty of stand-alone vSphere hosts. If you do have a cluster, how many hosts does the cluster have? What's your expected failover capability? (Note the use of "expected;" actual configurations sometimes don't provide the expected failover capability.) What's your workload profile? What's the planned growth factor for your workloads?
Basically, I found myself having flashbacks from reading the vSphere 5.1 Clustering Deep Dive book.
I love recognizing opportunities like this one. After all, that's what consulting is about. Not just answering questions, but helping people ask the right questions, and walking them through the solution.