I pretty much new tab every dang link... SO I never use breadcrumbs. In fact I don't care for them at all. I once removed both breadcrumbs and had a handful of complaints. People felt 'LOST' without it. It's like a "YOU ARE HERE" point inside a mall... So I leave it.
Some people scroll up to it, some people scroll down to it.
Haven't used it once. Not sure I have used the top breadcrumb either. I dunno, I have two habbits. One is to scroll all the way up and click at the forums tab, and two to open new tabs and type domains manually (with auto-completion).
I know they're there... But I never use them. In fact I often forget they're there. However, this is not to say others don't notice them. I think I removed them once and had a few people point it out (much to my surprise).
I was once told there is a SEO impact in removing them, but I'm not 100% sure how true that is. One person told me removing them is like removing double content and so its good.... Another told me its best to leave it for bots to easily crawl your site once they pass the post content. So 1 for and 1 against.
I tend to just scroll up and tap what's new again. I never really use the top breadcrumb either unless I'm purposely intending to go back to that forum and read another thread (that is, if I'm too far in a thread to just backspace to the previous page).
Create an accesskey for What's New and I'd probably use that constantly.