From some very preliminary research I am starting to believe that when you archive your posts at Blogspot versus using FTP blogging you do not appreciate the full search engine benefits that you do when you archive them back on your own domain.
I am doing a full blown two month test on this topic and so far just in the first week when comparing traffic results between my two blogs I am finding that hosting your blogs at Blogspot is second best.
One of my big concerns so far is that I can not see some of my posts on my Blog-World Watch where from the same day I can see my posts from Web-World Watch appear in the SERPs. Plus I do a weekly Google Sitemap for my Web-World Watch blog, but can not do one for Blog-World Watch as it is hosted at Blogspot and have no server access.
So my hypothesis is “You will not appreciate any significant search engine benefits from hosting your blog files at Blogspot and will when you use FTP blogging and archive posts back on your own web server.”