Beersmith is awesome! I would wait to buy it though. Version 2 should come out in June.
If you buy a pre-order of the software you get a free copy of the previous version to use until it comes out.
I'm pretty new to brewing but I like his book so far " Homebrewing with beersmith". He is good at explaining the whole process even the complicated math equations and figuring out these calculations with other methods if you don't understand the math. I only have a few books that came with my homebrewing kit, so not a lot to compare it to but I'm halfway and like it a lot more than the others I have read.
I also have a lot of respect for Dr. Smith. Although he does promote his software in the book he tells you how you could do it without the software. Several times its quoted as saying something similiar to: Beersmith software will show you the best hops to use for a recipe, or just do a google search for a hops chart.
Just out of curiosity has anyone used it with wine in a linux enviroment? I have mac but mostly use linux and try to avoid wine but I guess since it has a trial I could try it out.