Blogs and Blogging...
Thanks, Collagemama, for letting me know that the blog was looking strange. I hadn't noticed it because it didn't show up on Firefox which is my browser of choice. However, in Internet Explorer, the left margin of the posts was definitely messed up.
Take my advice, folks. If this ever happens to you, view individually each post that appears on the main page of your blog and determine if one of them looks wrong and all the rest are perfectly normal. Had I done that first, I could have realized that the very top post on the page was causing the problem.
But of course I didn't try a logical process of elimination. Instead, I started looking at the template. I found a small error there which I fixed, and I guess that made me think that the rest of the problem was in the template too. I searched until my eyes crossed.
I even ran the template through an HTML validator. It found over 100 errors, most of which are caused by scripts and by Blogger symbols for the different elements of the blog. It was not very helpful, considering the amount of time I wasted trying to figure it out.
Finally, I tried what I suggested above, I looked at each post individually -- and found the one problem post right away. Now I know -- DIV tags, used by Blogger for centering, confuse Internet Explorer when they occur within BLOCKQUOTE tags.