We use it where I work and the designers like it a lot. It works very well to build cross-browser layouts in a very quick and simple manner and has drastically reduced the amount of time it takes them to cut PSDs into raw XHTML/CSS.

One downside you will quickly notice is your markup becomes much less semantic and a lot more cluttered with CSS classes. This is simply by virtue of how all "grid" CSS frameworks like this work - they set up a ton of generic styles that are impossible to be symanticized. With blueprint you start to see a lot of classes that look like "span-XX last" or "push-XX" or "pull-XX".

There are a number of ways to get around this, however. The first is a tool that comes with blueprint that lets you set up a yml configuration which maps semantic ids to these generic CSS classes. For instance you can say "#footer => span-24 last". This will then generate the CSS in a semantic manner so you can continue using id references in your XHTML.

The second way, and this is the approach that I would highly recommend, is to go ahead and use some sort of CSS metalanguage/compilation tool such as SASS (Syntactically Awesome Stylesheets - http://haml.hamptoncatlin.com/docs/rdoc/classes/Sass.html). Chris Eppstein has done a fantastic job with the Compass CSS Framework (http://wiki.github.com/chriseppstein/compass) which builds on top of SASS, which allows you to do really amazing things with CSS.

The compass framework he has built allows you to do things like define CSS constants (colors, font sizes, etc), perform unit arithmetic, as well as define abstract classes or groups of properties called "mixins" which allow you to abstract out a lot of your repetitive CSS properties. It is also a whitespace sensitive DML which makes the highly nested nature of CSS selectors a breeze to work with. It also already comes with modules for blueprint and other grid frameworks!

I would check out his talk about it here if this sounds interesting to you:

http://pivotallabs.com/talks

HTH!

It's everything it claims to be, and really does make things easier. I can't recommend it enough.

But be carful: using blueprint as they recommend litters your markup with pseudo "inline style" classes. If you are a stickler for clean html/js, there are tools that compile blueprint into your custom css classes and ids. Compass is a great one for rails. I think blueprint also has built in tools for this now as well.

I used it here:

http://www.squeezedbooks.com

and here:

http://www.welton.it/davidw

I'm pretty happy with it. I regularly tried to do my own CSS, coming up with something I thought didn't look half bad, and people would tell me it looked awful, so I figured it was best to just use something out of the box that looks 'ok' to most people.

Maybe it is besides the point, but I use YUI grid. Not tried Blue Print CSS, but it took me less than a couple of hours to get hang of YUI. Never looked back.