Do I need to create more than one Adsense unit if I plan on using the same style of ad on multiple sites, or can I use the same code across multiple domains?
You can use the same code across multiple domains. But you want to see from wich domain comes more clicks and so it is better to make separate codes and name it different ( something like: text_ad_domain_name).
Thanks for the reply. What about using the same code, but adding separate url channels for each domain? I think this should allow me to track each site's performance.
I don't know, maybe you can do that. But I use for every placement a separate code let alone a seperate domain, for better understanding.
the code has an ad slot number.one channel per ad slot.you have to create the channel and an ad slot. you can use the "old adsense code",then you can just change the channel number and also change the color and size on the fly.
Create new ad codes for every new domain because i think you have your site with different colors and style so if you use same codes for every domain then you will neather track nor focus on your earnings...
You can use the same ad on all your site if you want but at least set up channels to track where they are located.