Rich Skrenta provides some tips:
# A conventional attack against Google’s search product will fail. They are unassailable in their core domain. If you merely duplicate Google’s search engine, you will have nothing. A copy of their product with your brand has no pull against the original product with their brand.
# Duplicating Google’s engine is uninteresting anyway. The design and approach were begun a decade ago. You can do better now.
# You need both a great product and a strong new brand. Both are hard problems. The lack of either dooms the effort. “Strong new brand” specifically excludes “search.you.com”. The branding and positioning are half the battle.