I purchased a license for sh404SEF today, and installed the lastest version (1.5.3.296). As I was playing around with the settings I noticed that the 404 redirection didn't work on my site anymore. If an incorrect URL is entered, sh404SEF redirects to the front page of the site. This is not good - as Google will not reindex the wrong URLs. It might also lead to unwanted URLs being indexed.
For instance, a person could link to a site like this: www.companyname.com/thecompanysucks/, and get the URL indexed in Google, showing the front page when clicked. Not very nice for the site being linked to...
Downgrading to an earlier version of sh404SEF worked fine, and the site is back to normal.
The problem is being discussed in the sh404SEF forums here - but no answer has been given by Anything Digital yet. I advise you to hold off on the upgrade until this issues has been sorted out.
Note that this problem applies to version 1.5.3.296 of sh404SEF.