Have to admit
I thought that part of the reason for reformatting HTML 4 into XML - e.g. XHTML 1 - was so that there would be less ambiguity about how tags should be "understood" by the browser.
Everything has to be closed so the browser doesn't have to worry about whether <p> is followed by </p> or not (for example). Therefore less bloat in the browser - smaller, better/faster browser.
A lot of what HTML 5 does is says, "OK, we give up. We KNOW you useless, talentless web-monkeys are just incapable of writing well-formed, semantic code - so you can have HTML 5 and write tag soup for all you're worth AND call it standards compliant - go you!" But that's been the case with HTML all along.
There are however some good things coming in HTML 5 - like the <nav> tag to semantically mark up navigation lists. And HTML 5 will still support XML style well-formed tags (as well as HTML 4 style). A default language for <script> isn't a bad thing and neither is the shortened DTD link line.
To be honest - if you're already coding to XHTML 1.1 Strict - you could simply change the DTD link and it would probably parse as 100% compliant HTML 5. So you can continue to write GOOD code with HTML 5 but you get a few new tags to play with.
Browsers won't be able to strip the bloat though so I'd guess HTML 5 will probably take fractionally longer to parse than XHTML 1 strict (assuming that XHTML 1 strict has ACTUALLY been written and the browser isn't having to fall back to tag soup parsing mode).