I have download the demo from Gamersgate, and put the game through some paces on lower-end PC configurations to test Jonathan's statement that you'll need quite a high powered PC to run it well.
Turns out he was mostly right, but not all hope is lost. Here's what I found out playing first few levels:
I installed the demo on a first gen MacBook Air, the one with 1.6Ghz Intel Dual Core, and an Intel GMA X3100 graphics processor. This is probably one of the worse computers around when it comes to gaming. With Windows 7 Beta installed with Bootcamp, I found Braid demo actually quite playable on it, but it had a noticeable (but fairly consistent, which made it better) frame skip everywhere. I'd say it run at about 20FPS on the level selection screen, and maybe 25FPS on the first few actual levels. Level selection screen has more stuff going in the background, so this is not surprising. Again, game execution speed was not affected, there was jut frame skip. Because of that I found the game playable, even though obviously a far cry from the intended 60FPS smoothness. Another thing worth noting is that making the screen smaller in settings didn't improve performance one bit.
On a PC with P4 3GHZ, with Nvidia 6800GS, I expected the demo to run better, because Jonathan said the game is mostly GPU intensive, and not so much with CPU. However, I found it originally pretty much unplayable on this config - mostly because it wouldn't skip frames. There were no frames skipped, but the game run probably 3x slower than intended.
*edit* However, this all changed when I used
-no_vsync_test
command line option, mentioned in developers blog. When I started game like this, it run so much better, frame skip was there, and I think it must be running at about 30+FPS now.
So, overall, I got what I wanted - playable Braid on my laptop, and I'm happy enough with it. Now that I saw it running on these two machines, I think Jonathan should have probably not said anything as he might have discouraged people with low end PCs from looking into this game, whereas actually there's no reason not to. Everyone interested should at least get the demo and use it with the command line option mentioned above.