OK, Steve wins the prize...

At the top of each of your posts is an empty div tag. Inside that tag is a style attribute with a clear: both rule.

That is what is causing the problem.

Turns out that in Blogger under Settings --> Formatting there is a setting for "Enable float alignment".

That setting "Allows image and text alignment options using the <div clear:both> tag. (Choose "No" if you are having post layout problems.)"

It was turned on, now it's turned off and things work right again.

Thanks, Steve.