We had this (radiant barrier) done to our house just last week. Yes, it does increase the heat at the shingles; however, those change are rather small (around 5 degrees). From the homework I did prior to choosing this approach, the benefit of using radiant barrier is mostly realized by areas in the south. Along with the radiant barriers, baffles were installed followed by the the insulation. One of the benefits I discovered while researching the radiant barriers is the increase in R values realized by using the radiant barriers optimized. Although the radiant barriers themselves offer no R value, the addition of the radiant barrier to insulation increases the R values of the insulation. For example, R-13 insulation used in conjunction with a radiant barrier increases the overall R value to R-21... likewise, R-19 becomes (as my memory serves me) an equivalent of R-28.
http://www.radiantguard.com/studies/TVAPerformanceTesting.pdf (old but worth reading). I read several more that were NOT from the manufacturer's website as they are often somewhat skewed.
Radiant Barrier | North American Renewable Energy Directory NARED
The difference we felt was incredible. Note: this project was for a garage/attic addition to our house (24' X 40' garage with a 10' X 40' room above the garage). I can shoot some pictures if you are interested.