On SMF 1.1.11 this is a problem, since there are 2 breadcrumbs instead of one, making each page have a repeated h1 tag - considered bad for SEO (I think in SMF 2.0 there's only one breadcrumb so everything ok in this version).
I'm with 2.0RC3 and I have two breadcrumbs...one at top, one at bottom.
Just look at this topic itself, there's two...
Ok, maybe they've updated it in recent beta or RC versions of SMF 2.0, because in earlier versions there was just one.
Anyway, in SMF 2.0 the H1 tag is always the same - the header logo - so it is never duplicated:
<a href="http://www.simplemachines.org/community/index.php"><img src="http://www.simplemachines.org/community/Themes/smsite2/images/site/smsite_logo.jpg?rc2.1.1" alt="Simple Machines Community Forum" /></a>
The H2 tags match the News, the H3 are somewhat strange (haven't understood them yet), the H4 match the Profile part in each post... and it's the H5 tags that match the post subject.
H2, H3, H4 and so on can be duplicated (or even more) without SEO penalty, it's the H1 that has to be in each page just once, so no problem at all with SMF 2.0.