Most leaks are due to installation error.
Most common areas for leaks;
1.Walls,Valleys,Chimneys,Skylights and vents.
Most common reasons for leaks in these areas;
Walls-....No step flashing,improper fastening and placement of the step flashing and the wrong size of the step flashing that meets the wall.Reuse for multiple re roofs.
Valleys-Improper lace.Nailing too close to the center of the valley,walking in the valleys,Inadequate lap of the leading side in the valley.Cutting into the valley when cutting 2" from the center.
Chimneys- No step flashing or inadequate size.Corners were not sealed,improper nail placements,Improper step flashing placement,reuse of flashing,faulty counter flashing,busted mortar joints,worn out pan on the back of the chimney.Improper installation of the shingles going across the pan.
Skylights-Cracked domes,reusing step flashing,sealing,worn aprons and pans,shingle sequence installation.Inadequate curb.
Vents-Damaged vents,improper shingle installation sequence,improper fastening.Reuse for multiple re roofs.
Pipe flashing-Improper fastening,improper shingle installation sequence,Dry rotted/weathered collars,faulty product.Reuse for multiple re roofs.
Furnace pipes-Improper fastening,improper shingle installation sequence,not sealing the shingles to the flashing beside and behind,damaged/missing cap,damaged/missing collar and reuse for multiple re roofs.
But like everyone said roofs that were put on in 08' should not be leaking.But like it was already stated you should contact the manufacture and see if a inspection might be warranted.