Shortbus, it's looks like it's been over a month since your post. Any insight?

There are several factors that will determine how effective the product search will be.

1) Are you sending in a fresh feed daily?
2) How well are your products categorized?
4) Are your products titles and descriptions written in such a way that they contain the keywords or phrases one might use to search for that specific product, ie. colors, sizes, etc..
4) Are you making use of all attributes?(If so, great, now it's time to start making use of "custom attributes")

For those interested in suggested attributes for products, start here:

Google Base Attribute List: Products [base.google.com]