When inserting codes into the Blogger template, page element, or blog post, you may have seen error messages that the code could not be parsed, was not well-formed, was broken, or that the elements were not closed properly. These errors can be corrected if you understand the rules that must be adhered to in XHTML documents.
Regarding blogging I think that engaging the readers is very important.Blogging is getting easier by the day. But many times I have found that blogs can be hard to maintain.
Yes learning some xhtml can be very helpful for most bloggers.Another good blog for tips and tricks for bloggers is the google analytics blog.