If you've read the Android Police review, he experienced some pretty awful lag especially with side by side apps, and took video of it, so it's legitimate. I think the question is more why the inconsistent experience (and Samsung really didn't do any extra QA on the review units? That's shocking). I'm glad folks here aren't seeing the lag, though, because my wife's looking to buy one of these for note taking once the LTE version is out, and I was starting to feel like I was going to have to dissuade her.
Here is the link to the Android Police review, for those who're wondering. I trust these guys to give a legitimate review, so there must be some real inconsistencies in the devices that are being sent out.
No offense to @mmaestro but don't visit the site. I think the reviewer was going for that "shock" factor to draw people to his site. At one point he recommends getting the iPad. There are sites that try to remain objective, like ZD Net, but they are clearly biased towards iOS (as well as other popular blogs). But if you are an Android site, you have to at the very least give the benefit of the doubt.
If you focus on what Samsung is trying to do with the Note, and it's features, you would be impressed. Instead, other blogs, this one included, want to talk about the plastic feel, or the 1280x800 display, or TouchWiz. And just about every reviews compares it to the Nexus 7. A fine tablet, I have one, but the N7 and Note 10.1 are two different animals.
I agree with @mmaestro that some reviewers got bad devices; it happens. But as a professional you need to look past that and focus on the product itself. And I'm using that term "professional" very loosely when it comes to some writers on some blogs.