I'm also in the save 20% crowd, unless there is something very unique about this house.
For instance, we moved into a house and paid 5% down. It was everything we were looking for in a house, had a motivated seller who sold under fair market value, and it's 3 blocks from my job, so I walk to work daily. That made PMI worth it to us.
Having said that, PMI totally sucks ass. As others mentioned it's easily the most worthless thing you'll ever pay money towards. What we did to fix this was we paid 15% of our mortgage over 10 months and then went through the process to get PMI removed, which was an application process and a new appraisal.
Since it sounds like you haven't dialed in on a property, I would just wait the 6 months to have 20% down. Yes, interest rates might rise a bit, but then you won't have the hassle of PMI. Even with our aggressive repayment, the PMI and appraisal cost us around $1000 for the 10 months we had it. Furthermore, every lender is slightly different. In the mortgage papers, it lists good payment history as a condition to remove PMI. I know some lenders won't even consider this met until you have the mortgage for at least 2 years! Ours told us that paying off 7 1/2 years of the mortgage in 10 months was suffice.