I don't know about the EU, but in America I don't think it will do much at all. Only a very few of my real life friends know what KZ2 is. Combine that with the lack of advertising you will get fewer sales.

Yakuza 3 will probably push more units IMO.

A short boost, maybe big too,(*) but most people are expecting a price cut.
Sony doesn't need to do a big one, just make potential buyers stop waiting for it, the total during the current year shouldn't exceed 100€ in EU, but in April they could at least lower the MSRP to the current average shop retail price, that is roughly 370€ now, so a 30€ cut in Spring and a 50-70€ cut in mid Autumn.

(*)Edit: possibly followed by a permanent 10-25k WW boost

In Europe it porbably will in US dont know.

In EU it will boost up HW sales, not looking as good for NA though.

I don't see any reason why we wouldn't see semi big increase in FPS loving america.

I think that ps3 to x360 gap will be much smaller for next few weeks at least.

I agree: as KZ2 somehow fills a gap, it should give good results where FPS' are more popular. So, although it's very unlikely it will beat XB360 in US, nonetheless US sales will benefit.
So PS can easily temporarily beat XB360 in EU thanks to KZ2 and in JP thanks to Yakuza 3, in USA it's very difficult, worldwide chances exist and aren't neglectable, but it's by no means granted.

10-50% boost world wide for the next month.

I don't believe in any measurable boost beyond that period of time.

That translates into a 60 000 - 300 000 boost in total.