It is my understanding that your body will treat SFA and MUFA very similarly, as neither are prone to oxidation and both are healthy sources of dietary fats. There's no real need to watch your MUFA intake, save for the fact that most MUFA comes packaged with at least some PUFA, as Paul alludes to in his answer. In some cases, especially with some oils, MUFA and PUFA are about even. Those are the oils you'll want to avoid, with one exception, cold pressed sesame oil, which has some poly, but is rich in anti oxidents so it is not prone to oxidation.

Optimal Ratio: I would say get at least 90% of your fats from a combination of SFA/MUFA and less than 10% of your fats from PUFA.