This is a great idea; however, let me set some expectations for the community regarding the cost of producing an ASIC. With ASICs, you have four different choices:

1. Academic "wafer sharing" - this lets you get a very simple design fabricated on a very "old" technology. Wafer sharing doesn't allow for large volume production - it's for research projects. However, wafer sharing is cheap.

2. Structured ASIC - http://en.wikipedia.org/wiki/Structured_ASIC_platform; this lets you relatively easily transition from an FPGA to an ASIC design, using a chip that has the first few layers already populated with an array of standard logic. Essentially, you just provide the wires to connect up the logic in the way you want it. Expect to invest close to $1M to produce the first run of a structured ASIC design.

3. Standard Cell - http://en.wikipedia.org/wiki/Standard_cell; this lets you build your own ASIC by assembling networks of standardized components. All of the layers of the chip are up to you. The cost of a standard cell design using recent processes these days is $5M - $10M.

4. Full Custom - Faggedabahtit; full custom designs achieve the best possible performance, but rely on literally designing the entire chip from the ground up. Companies like Intel use full custom processes to highly optimize their processors for the absolute maximum performance. Cost: $100M and up.

Given these four options, a community designed ASIC is probably best served by the wafer sharing model. However, if enough people can put their heads together to raise $1M or so, a structured design would definitely provide the best ROI. If Bitcoin explodes in popularity and the mining / transaction reward can be measured in $10Ms per month, then standard cell or full custom designs will be funded easily.