We have a full Cognos environment here (10.1). The products are different and they shouldn't be thought as "only this one or that one". Cognos and Business Objects are of the "one or the other" category. Tableau gets things done now and with little-to-no IT interference. Cognos is ripe with IT interference.
- No Excel plug-in. Not necessary. For charting it blows Excel out of the water, no comparison. Much easier to use.
- Some audit capability. Not enough for enterprise in my opinion but each major version shows improvement.
- TM1 - N/A
- It is a dashboarding product.
- No rich metadata like Cognos. Which is nice when you need things done now and don't have time to wait on IT to get the ball rolling.
- No formal event-driven scheduling.
- Ad-hoc reporting is what Tableau is all about. Reports/dashboards can be saved and scheduled on the Tableau Server to become canned reports. People can subscribe to these reports to have them emailed.
- No multi-dimensional cubes like Cognos because aggregation is something Tableau does automatically and very quickly.
Tableau is far easier to install & maintain. I would imagine it's much less expensive as well. Tableau and Cognos (if going for the whole suite or close to it) aren't competing products in my opinion; each has it's strong & weak points and they help provide the user community a greater choice of tools to get the information they need in the time they need.
In times gone by, I have to say, I was very plugged in to the IBM toolset.
Requirements Cycle: IBM/Telelogic DOORS
Modelling: Rational Rose
Database Admin: DB2
BI reporting: Cognos
Most of that has now been replaced by SQL (Postgres, MS and My) with Tableau, QGIS and R. I can see the day soon when R and GIS is fully "rolled in" to Tableau (with Alteryx); and the dBs can be of any type, anywhere.
I am sure that the ROI of Tableau (with Alteryx) now surpasses Cognos - my development time and publishing times have compressed very nicely over the last year, with a shallow learning curve. I'm saying this with little bias - I still have a copy of Cognos, ESRI and DOORS on my machine, but they are getting less and less "click time".
The one IBM product that still gets hammered is SPSS, and I don't see that going away anytime soon. I see IBM more as a specialist consultancy practice now, rather than a product focused company. But Big Blue does have some advantages. The main one for me is the ESRI -> Cognos GIS connector.