I use Jammer (Ver 6) for a number of purposes. I originally got an earlier version (4 I believe) from drums, bass, keyboards to practice guitar with. The variety of styles and genres was useful for expanding my skills. Then I started to use it for building bass and drum tracks for my own compositions. Initially, back in my days using Home Studio, I would play Jammer through an external synth and record the tracks as audio in Home Studio. As I moved up to Sonar I started importing MIDI files to trigger EZ Drummer kits and then Addictive Drums. I still find that there are some styles where the Jammer grooves work better than the styles available in either EZD or AD, particularly swing, latin and reggae grooves. I will also use Jammer to create bass lines when I need something more complex than my rudimentary bass playing can deliver. I have been using Jammer for years and I am comfortable with the interface so I do like it and I have certainly gotten great value for a relatively modest investment.
Also, I got an e-mail from the Jammer folks a few days ago that indicated they were climbing out of the recession and were starting new development. I don't know this for a fact, but I suspect this is a second business for some musician/programmers whose efforts were being spent keeping themselves fed, housed and healthy over the past few years. I'm glad to see it looks as if they're back at it.