This is quite a common topic to come up - wanting to use a custom host for a blogger blog. My personal reasons are due to issues concerning iframes, SEO and the specific address of the blog.
I have the custom domain already, and I am familiar with the necessary steps to use it with blogger (quickly outlined in such resources as http://www.wikihow.com/Use-Your-Own-Domain-on-Blogger.com)
My question relates to the manipulation of the DNS administration.
I do not actually know what the A and CNAME records do. Moreover, the step requiring the CNAME record attachment of ghs.google.com produces an error, as it conflicts with a previous CNAME record already listed (duplication of records). I could delete this extant, conflicting record, to attempt to solve the problem - but I would be doing so blind and may consequently move from what is a slight inconvenience, to a very serious headache. I am also wondering if there is any security risk in this pointing operation, as I have seen no mention of it either way so far.
One final issue, albeit one which I am not overly concerned about, is whether this pointing could interfere with other pages in this domain (if I opt not to use a subdomain).
Perhaps I am not entirely understanding the process: how will the address of the blog change if the location of its files (and therefore the blog itself) does not?