First point : You may add a "create an adsense account" sponsored link (wich refer to admin id) near by the field "enter your account ID".
There is no small profit, and I'm sur if you help your member to make money from their blog, they would register and activate the plugin.
Second point : the request from Bike seems to me very important, even more when you add ads to the theme. 3 ways to solve that :
- you don't display add if the member don't add his account ID. You may loose money, and you're hosting a blog for free.
- you display a message to tell the user to enter his account ID. In this case, it's seems important to me that, if the user create a Google AdSense account, he made it throught admin sponsorized link.
- you display ads with only the admin id. You may add a message "register your adsense ID and start earning money from your blog", but only if the member is connected to his blog (visitors don't need to see this). Again, if user register to adsense, it must be with your link.
Third point : possibility to hardcore AdSense options (color, size, ...) depending on the theme. Admin may see a list of theme, and configure adsense option for each theme (you should be able to add 3 different format for ads, and 2 for what is called in french "ensembles thématiques", as it is the max possible on a page). Not everyone is familiar with adsense, so something you just need to enter your id should be great in order to optimize ads on the blog.
By the way, thanks for your plugin.