Wow, if people read all this to make an informed decision about an Apple product, they'd walk away grossly misled and misinformed.
The population at MR probably represents less than 1% of the total user base for any Apple product. People who post here are either those who want to find a problem, or those who want to convince themselves that there isn't one. The majority of the people using these products wouldn't even care about the issues we dissect here at MR.
The absolute zeal with which people stand by their opinions here is commendable, but it ultimately leads to a dichotomous result. Therefore, if someone from the other 99% comes here looking for an unbiased and objective opinion, they would almost usually walk away with more ambiguity than before.
Having said that, I personally feel this lag issue has been completely blown out of proportion. I agree with some people in this thread, that if this thing can manage D3 at 2880x1800, then its quite obvious that the hardware isn't whats causing the "so-called" lagging while browsing certain websites.
Also, the part from the AT review has been completely misconstrued and used out of context. Read the whole damn review; the rMBP is the 1st Mac to ever get Bronze Editor's Choice Award at AT.
Moreover, to return a $2199 machine because the News Feed on Facebook doesn't scroll smoothly is an indicator of just where some people's priorities lie while buying such expensive equipment. Someone above me had a brilliant response; if Facebook is the objective, then why not buy an iPad and save a ton of money?
Anyone who has been using Rev 1 products should know that its a gamble, and that owning the latest and greatest always comes at a price. So the moral of the story is, stop whining and stop wasting time analyzing things that don't need analysis.
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Jeez guys. Way to go off topic. Read my original post, and please don't post here if you're just flaming/baiting/whatever. Looks like I need to ask this question on a more useful forum.
To answer your question, yes, this most certainly seems to be a software issue, and from the looks of it, the ML GM seems to fix it to a certain extent. It is highly unlikely that things can get any worse from this point on.