I recently started a blog on wordpress.com, but I didn't want to rule out monetization so I had to move the data I had already entered from there to blogspot.com.
It was very easy to do using this webpage which gives detailed instructions about how to proceed. You basically export your wordpress blog as xml, upload it to the conversion tool, and then download the converted xml blog data. Then you import that data into your blogger blog and you are set.
I'm not sure if comments transfer properly as I didn't have any since the blog was so new. Wordpress blogs have tags and categories whereas blogger blogs only have labels so both tags and categories become labels. It isn't a big deal since you can customize a label widget to only show links for selected labels (presumably just your categories).