Hi Velvet Blues
Great plugin, helped me a lot!
The only thing I'm missing (or I did something wrong ....): strings in wp_options don't get updated. The symptom I see is that widget contents, which are stored in the wp_options, are not updated, although they where containing strings, that I entered as "Old URL's". I.e. miss-typing can't be the problem. In fact at all other occurances of those strings where properly exchanged.
Is the content of wp_options being altered by your plugin?