They're prepared a themes directory for you.
Creative coders have since already released two easy to use iGoogle theme editors – for you.
Google has assigned a 50×100 pixels attribution area in the top right corner of the footer of a custom theme for you to brand yourself or your client.
There're 19 themes so far — all made by Google.
What are you waiting for?
Bonus tip: prepare a tab with solid widgets geared toward your market and use the "Share this tab" feature to package it (with your own theme?!). If some of those widgets are your own — your impact just went up.