There are some ineffeciencies when creating reports, such data grouping. You have to click and group each data column separately.
The security features tend to slow processing times down significantly. However these features may only be an issue due to our SAS provider controlling them. May not be an issue if you own the Cognos software.
This software is a part of the package that comes with our Human Resources software, therefore we will continue use of Cognos. However I am not disappointed in the product. I would not hesitate to use it even if we had to own it outright.
Make sure that any custom tables that you have, are built into your metadata packages. You can still access them via SQL queries in Cognos, but it is much easier to have them as a part of the available metadata packages.
If you have used any reporting software before (such as PeopleSoft or Crystal) it is not too difficult to figure your way around in Cognos. However if you are totally new to BI software, you should go for formal training. One-on-one is ideal, but classroom training is also very good. I purchased IBM Cognos 8 Business Intelligence: The Official Guide: 1st Edition, which I used to get a lot of my information. We also utilize the internet when we are not quite sure about how to do something. YouTube has some good training videos, and also there are a couple of blog sites that are very helpful (www.cognoise.com and http://it.toolbox.com)