Have a look at video 2 - it has all of the RAW image processing capacity of PhotoShopCS2 plus some more, and add to that you canapply all the same options to other formats too !!
The huge plus to my way of thinking is that everything you do in this app is completely non-destructive - it doesn't touch your original files at all. All editing and correcting that you do is stored as scripts within the database and only applied as you output a fresh copy to load in Photoshop. This all happens transparently so it means you can edit and change a photo and save copies of it without ever altering the original in any way at all (whilst still retaining all the processing you have worked out). It is really cool and ACDSee doesn't do anything like this.
The other really cool feature is the library organisation. You can leave all you images in the folders they are in at the moment or allow the app to reorganise everything (the way you want because it is completely customisable). Either way the internal organisation for the app is held in its own relational database meaning that you can organise your photos into 'shoots' and 'collections' as you want, apply multiple tags really easily (by drag and drop) etc. To me this gives real multidimensional flexibility (and not just a tree structure like most othe picture browser setups including ACDSee).
Don't get me wrong - I have bitten the bullet and upgraded to ACDSee Pro not so long ago, and they seem to ironed out the problems I experienced before but Lightroom looks to have the potential to make ACDSee look like DOS compared to Windows.
Maybe I am getting overexcited (especially since I haven't played with it) and doubtless it will be horrendously expensive (which will be really frustrating as a lot of the RAW workflow functionality is from code lifted straight from Adobe Bridge which I already have).