Okay, so I looked at this. I don't get the point of the grid system. Rather, what I want to know is: if you're going to laboriously simulate tables in CSS classes, why not just use tables? It would be simpler, more easily understandable by human readers, scales up and down better (Blueprint doesn't do non-fixed layouts yet, apparently), and in HTML4, at least, would usually involve less markup.
Against this, it wouldn't be quite as easily read for the tiny fraction of a percent that use screen readers. That seems like a very small price to pay for the major wins.
The grid techniques help to define content regions and to help separate your layout from your information / data. Tables were created so that you could layout out tabular data / information for presentation.
There hasn't been much in the area of css frameworks besides for YUI and this framework is based on the work of some well-known designers. The nice thing about this and YUI is that it does help with consistency from browser to browser and it gives you a similar vocabulary to use.
I'm sold on the grid technique in general but I'm not sold on either YUI's grid.css or Blueprint's implementation but they're both very good starts.
Someone correct me if I'm wrong but I guess what blueprint and yui (http://developer.yahoo.com/yui/) buy you is consistency across different web browsers. Tables with applied css (or their own attribute may behave differently depending on what browser is viewing it)
I like the reset.css approach that both frameworks use. This will normalize your document so that it looks the same in various browsers. Then you can start re-building your look using their guidelines and the fonts.css or typography.css and to create consistency across common browsers and operating systems.
It's quite amazing how different a blank html document with an h1 and p tags looks from one browser to another let alone from one OS to another (margins, padding, etc). The examples with both frameworks give you something to try out before you use it too so you can see how it will look.
Against this, it wouldn't be quite as easily read for the tiny fraction of a percent that use screen readers. That seems like a very small price to pay for the major wins.