Google's Brian B. posted a confirmation of the issue, he said:
I've seen a number of reports from users that links to My Maps bring them to blank maps. This seems to mainly be affecting people using Internet Explorer. I want to let you all know that the team is actively working on a resolution to this problem. I'll post an update here as soon as I have more information. In the meantime, some folks have found that pressing the "back" button on the browser is a temporary workaround for them. You might also want to try using another browser.
I confirmed the issue myself.
My Maps results in Firefox:
My Maps results in Internet Explorer 8:
The left hand side is missing.
This seems to be a large issue for many sites who use My Maps as part of their service offering.
Forum discussion at Google Maps Help.