Two days ago I did the 70-445 exam in beta (TS: Microsoft SQL Server 2005 Business Intelligence - Implementation and Maintenance). I cannot talk about the exam content, but I think I can talk about the exam in general.
As usual, an exam allows you to study many topics you don't cover with your daily tasks. For example, the exam cover some aspects of the delivery of a solution (SSIS/SSAS/SSRS) that needs some study, because even if you have years of experience, you may have not encountered all possible scenarios, especially if you work for a single company (a consultant may have seen several customers scenarios).
The difference between TS (Technology Specialist) and PRO (Professional) versions of the exams should be this: TS are oriented to implementation and delivery of a solution, while PRO are dedicated to design topics. I will test the beta of 70-446 exam (that is the PRO version of the same thing...) in a few weeks. The preparation guide talks about deploying and optimizing SSAS solution, topic that is not covered by the 70-445 exam (even if it cover the development of a SSAS solution).
As usual, the validity of an exam based on automatic test is limited, but I think that who has real-world experience should not have many problems passing these exams. The major difficult may be that you have to cover a large set of products (SSIS/SSAS/SSRS) while in my experience it's easier to find people who are more experienced on a single topic (in particular, the wider distance is between who develop SSRS reports and who builds SSIS packages).