Alex Iskold has a great post on Read/Write Web about Google’s Custom Search Engine and how it shifts the value in vertical search from infrastructure such as crawling and search relevance to UI and site selection.

I completely agree that Google CSE is a net positive for the vertical search space. However, it’s important to keep in mind that it only allows you to focus on finding web pages restricted to a specific slice. Having the crawling and search relevance components freely available is a huge boon to new entrants. That stuff is really hard. However, Google CSE doesn’t help you when you’re search for domain specific items that aren’t web pages e.g. products, flight information, resumes etc.

For example, take Couponlooker, which is focused on helping people find online coupon codes. If you search for “amazon coupon codes” on couponlooker, you’ll get back actual discount codes with expiry dates.

Couponlooker Results

If you do the same search on a Google CSE, you’ll get back pages with coupons on them. A subtle difference to be sure, but it’s extra distance between the user and their goal.

Google Results

Google’s Custom Search is a pretty incredible product, but you’re limited by the underlying infrastructure and search semantics. This is not a bad thing - the guts of the system are incredible and for web search haven’t been beaten yet. If you’re looking to do something different though, you’ll probably need another approach.