Hm, that is annoying, yes..
I know there was a similar case with that theme some time ago, but I cannot find the thread.
My first guess is that you have added something with "hidden" formatting. Please do not paste from Word or similar editor. This might be useful
http://faq.wordpress.com/2006/11/09/why-not-to-use-word/
Try to remove the last post you added, and see if it returns to normal - then you know where the problem is, at least.
This might help
http://faq.wordpress.com/2008/05/30/why-is-my-sidebar-at-the-bottom-of-my-posts/
Even if your sidebar is not at the bottom, but in fact seems to be gone, give it a go.
I checked your blog in firefox, opera and safari. Looks the same in all three.