I just ran into the problem already described here. It's a weird situation: Status bar displays black text on black background. So all it can be used for is as a progress bar.

But I found a solution, and I wanted to let others know. Since I didn't want to sign up to that forum, and since the OP there hasn't posted there in over two years, I'll post it here instead.

It's simple: Excel displays the status bar correctly if you include certain Unicode characters in the string, such as the following:
[vba]Application.StatusBar = ChrW(&H2027) & "Hello world!" [/vba]