Yes, I've worked with Mechanize quite a bit.
I like it for interacting with nice vanilla web pages. I don't know how to use Mechanize to handle websites which pop up additional confirmation dialog screens. I'd prefer Mechanize to OLE + IE, but I've unable to drive complex websites with Mechanize. (Could be the problem is me, not Mechanize -- I'm well aware of that!)
What I really want to is use automated intelligent perl scripts to interact with complex HTTP and HTTPS web apps designed for IE or NN. I'd rather not use OLE + IE -- using IE is a hack; IE has a big memory and processor footprint; IE is Win32-only; IE object docs are cryptic; etc. But (again maybe due to my lack of skill with LWP and Mechanize), OLE seems the most feasible option....
