Unfortunately, Blogger native commenting requires no commenter information, beyond the basic authentication used - when we require authentication. And what authentication that we might require isn't going to provide any definitive identity information.
Blogger commenting provides 4 possible levels of authentication.
- Anyone - includes Anonymous Users
- Registered Users - includes OpenID
- Users with Google Accounts
- Only members of this blog
The top level of authentication - "Only members of this blog" - is applicable to private blogs, where hopefully we knew the blog members in some way, before we invited them to be blog members.
The top level of authentication applicable to public blogs - "Users with Google Accounts" - provides us a Google account name, and no more. The Google account name may be based upon an email address, but that is not a 100% reliable possibility.
The next levels - "Registered Users" and "Anyone" - provide still less reliable information. "Anyone" may include "Name / URL", at the option of the commenter - and only as accurate and useful as the commenter wishes.
If you want any demographic details about the commenters to your blog, you'll need a visitor log, such as SiteMeter or StatCounter. Even with SiteMeter or StatCounter, the accuracy will be limited, and details won't provide you with any personal identification, such as name and address.
The bottom line here is that Blogger Commenting is not going to provide any reliable, and uniquely interesting, identification details about anybody. Anybody commenting on a Blogger blog can rest assured - Blogger supports your ability to comment anonymously, just as they support our ability to publish blogs anonymously.