This may not be all that useful for hackers who aren't doing anything particularly weird. Wget <i>should</i> return the same thing. The times that this is interesting is when wget doesn't return the same thing. This could indicate a bug in your ip targetting, A-B testing, or browser-specific delivery. It might also help reveal problems like mentioned here <a href="http://news.stepforth.com/blog/2006/09/has-your-site-been-hacked-here-is-how.php" rel="nofollow">http://news.stepforth.com/blog/2006/09/has-your-site-been-ha...</a> where a hacker shows regular users the original page and shows googlebot a page filled with links to porn.
Hmm, for my site it seems to cut off at right around the 3000th line of source. Should I be worried about this? Is this a bug in the "Fetch as Google" feature or perhaps googlebot cuts off after the 3000th line...?
Awesome feature. I just wish you didn't have to have a GWT account to use it. A lot of webmasters who would have run it out of curiosity (and possibly found something wrong with their website) aren't going to bother.