Just be sure that you know the rules for your mortgage and PMI. When we tried to drop PMI I found that it wasn't as simple as I thought it would be. This is what happened to us:
We paid the mortgage down to 80%. When we called Bank of America they told us that we'd have to pay for an appraisal to make sure the house was still worth what we bought it for. They said that when we paid it down to 78% it would automatically drop. We paid it down to 78% rather than pay for the appraisal. We requested the PMI be removed again. They told us that we'd need an appraisal. We told them what we had been told and they said that our mortgage terms indicate that it will be automatically be removed when our original amortization schedule brought us to 78%. Since we had accelerated our payments, that would be a couple years down the line. In the end, we got the appraisal, had to pay a bit more to get to 80% after our home value dropped a bit, and finally removed PMI.
Long story short, at least some banks may require an appraisal which they'll charge you for. If you don't make value, you may not get the PMI approved. Your mortgage may not be in that boat but then again, I didn't think ours was either based on my initial conversations with BoA.