What do you like best?
IBM InfoSphere offers tools to build integration hubs and services for large scale enterprises.
Datastage and Quality step is a competitive ETL/MDM solution and is comparable to informatica. The performance and ease of creating multinode jobs to improve processing speed is impressive.
Integrates well with Oracle and IBM DB2 rdms. Has SAP support via plugin, but it leaves much to be desired in this area.
If you already have an enterprise license for IBM tools then this should be an obvious choice, especially if you plan on pairing it with tools like Optim for test data management. Works well if you also utilize Sterling Commerce B2B for file transfer management.
What do you dislike?
Terrible code version control. Two options:
 use CVS - really? 1990 called it wants its version control back
 or use IBM's proprietary version control system that doesn't integrate with your automated build system (such as Jenkins).
You can extract code as dsx (txt files) and store it manually in your preferred vault (svn, git, etc) but this is cumbersome and there is NO PLUGIN for these other control systems!
While cheaper than Informatica in many instances you will run into documentation/support issues. Sure you can pay for the enterprise support package, but when you need a "quick" solution and just need to scour the web for an answer, good luck.
For companies choosing to utilize the Integration technology like Datastage/QualityStep be aware it is extremely hard to find trained Datastage developers. Datastage makes up a small percentage of the US talent pool, meaning it is hard to attract and retain talent. So any savings you may get by going with IBM could very well be eaten away by the higher cost of human capital.
Recommendations to others considering the product
Good for cost savings if you own an enterprise license for all IBM software. Be wary of the lack of quick documentation and online support forums. Be sure before you switch products that you will be able to find talent. Outsourced talent is relatively easy to find for this product, on-shore US talent is extremely rare and expensive for experienced developers compared to the competition.
If you heavily use other IBM products you should at least consider this since it integrates well with other IBM tools. It however has lackluster integration with 3rd party tools like version control systems.
For a company that sponsors Eclipse, they have chosen not to use it as a basis for this suite of tools leaving its interface frustratingly stuck in 1990 by graphical standards and usability.
What business problems are you solving with the product? What benefits have you realized?
Integration of large datasets for thousands of batch interfaces. (Datastage)
Use of Master Data Management with qualitystep and qualitystage.
IIB (related technology) is used for real time interfaces. Datastage can do real time interfaces, but does not function well for real time file interfaces since jobs must be scheduled to constantly check for files.