To help everyone put this in perspective, to achieve >50% of the network hash rate while solo mining Litecoin, it would currently be necessary to fire up a GPU farm of around 23,000 Radeon 7950's.  Assuming 6 GPU's per motherboard, that would be around 3830 mining rigs.  So, the current bar for attacking Litecoin with GPU's would be around $6,670,000 for the GPU's alone before adding in additional support components or a facility and support infrastructure to house the operation.

Disclaimer - Someone willing to invest that amount would probably just fund the development of PCIe breakout/bridge boards that drive significantly more than 6 GPU's per motherboard though, so the motherboard count above is only based on off-the-shelf components and PCIe riser cables.  We prototyped a PCIe x16 to 16 PCIe x16 slot breakout board (only 1 lane actually connected per x16 slot) using an off-the-shelf PCIe bridge IC on a 4 layer board, and it didn't cost much to achieve operation of 16 GPU's per motherboard.  It certainly cost less than the extra motherboards/CPU's/RAM that would otherwise have been needed.

Note - The cost to design, tape-out a prototype ASIC, get in with a wafer aggregation service (like MOSIS) to fabricate a few dozen of your prototype dies, and have them diced and packaged, is well under $1 million.  If someone has a better approach for calculating scrypt that isn't bottlenecked on external memory bandwidth and were aiming at a business that would otherwise possess enough FPGA-based boards to 51% Litecoin, they would actually be way way ahead financially to go the ASIC route right from the start.  FPGA's are very costly compared to raw die area per unit of logic area, especially at high quantities.  Almost all the cost in developing an ASIC is up-front, after that it's dirt cheap to scale the quantities up.