What do you like best?
IBM Cognos BI is a highly flexible suite of report-writing and display tools to support reporting a variety of data in a variety of formats. Users can usually find at least one or two ways to do almost anything in Cognos, and for those features for which Cognos does not have any pre-set properties or solutions, users can bring in custom HTML items to add functionality to their reports. Many of the blog posts out there that look at ways to accomplish very specific, advanced things in Cognos will revert to modifying a custom HTML item in the report.
What do you dislike?
The learning curve for Cognos BI can be steep, and this is do in part to its flexibility. Because there are thousands of settings, properties, tools, and combinations of these things, there is not one set way to accomplish a task in Cognos. There are best practices, but these will vary based on the user's data.
Moreover, the documentation that IBM provides is considerably technical and is lacking in proper examples (though there are books out there that do a better job of providing real-world examples). The challenge with relying on community support forums to troubleshoot the report is that how you write a report is highly dependent on the structure of your data. Oftentimes, we have found that the best way to solve something in Cognos BI is to structure the data differently either in Framework Manager or (when working with dimensional cubes) in Transformer.
Whenever you deviate from very simple report requests, you almost become an explorer of yore, forging into unmapped territory (at least when it comes to your data structure). This, unfortunately, means that you often have to find your own way.
Recommendations to others considering the product
Find other users in your industry that have similar data marts and use Cognos for the same purposes that you are considering. Set up a call with those other users to ask them about implementation, organizational support necessary, ease of distributing reports to other users, and overall experience with the product. Also, invest in some of the Cognos books that are out there; they are, in many ways, superior to the documentation from IBM.
What business problems are you solving with the product? What benefits have you realized?
We rely on Cognos as our reporting system of record for all student data: admissions application, financial aid, registration and enrollment, grades, billing, and more. For the past 4 years, we have been been using the system for all of our detail list reports. More recently, we began using Cognos also for summary level reporting and will soon be using it to roll out dashboards to our campus colleagues.