This is simply an excellent book; quite possibly the best book I have read on analysis.
Martin Fowler cheats by actually being able to write. He has a very lucid prose style making this a very readable book (a strength that also manifests itself in his book UML Distilled) even though it deals with complex subjects.
The book deals with using patterns to address particular business areas. However, it has a great deal to offer anybody interested in analysis or modelling (whether they are working in the OO world or not) and provides one of the best explanations I have read of the purpose and objectives of modelling.
Each problem area is presented very clearly and a number of different solutions are presented at different levels of abstraction (and hence complexity) with lots of useful insight into the factors that would determine the appropriate model.
Analysis Patterns is a book that bears reading and re-reading. I frequently refer it as an excellent source of interesting ideas on ways of approaching complex modelling & analysis issues. I have never managed to take one of the patterns and apply it as is; however, the ideas and concepts expressed in the book influence many of my models (even when the business problem I am tackling initially appears to be entirely unrelated to any of the patterns).
Frankly, this is a book I wish I had written.