I'd like to request the ability to preview the extended entry in addition to the body. Currently only the body shows up in the preview even though the extended content will be part of the final blog entry. I can work around this by composing the entire blog entry in the body tab and then cut/paste the extended portion but it would be nice to have a way to preview it without doing that. I think it would be fine to simply render both in the preview since this is the way the full blog entry will be. Alternatively you could provide a popup button on the preview window that let the user see body, extended, and both.
I notice that it somewhat misleadingly selects the first item in the list in the Preview template for weblog popup button instead of the weblog you are currently previewing an item for. It does appear to apply changes to the correct weblog's preview but it would probably be nice for it to correctly select the weblog you are currently working with.