I've perused the Mac App Store. There are some nice apps in there, but I have to say that just based on the value to me being offered, almost every single paid app I've seen so far has been a minimum of double the price I'd be willing to pay for that app. I'd be happy to pay $10 for Daisy Disk, but not $20. Maybe $15 (more like $10) for Earthdesk, but not $25. The one exception is the Contact Cleaner and Calendar Cleaner apps. I don't know if they're any good or not, because my calendar and contacts are clean enough for me at the moment, but if, for example, I had my Mother's calendar and contacts, it'd for sure be worth $5 to fix them.
We'll see if the market as a whole shares my view. Early indications are that at least some developers who got in on the ground floor are ecstatic about first day sales, but I do suspect that, as with the iPod/Pad/Phone app store that preceded it, prices will plummet as we see a race for the bottom.