I agree with you totally - the software direction - that is. As you probably know by now (From Yahoo group) my hardware arranger is a Roland EXR-7 and my wife has a Korg PA80. I have three controller keyboards, Roland A-30, a smaller Roland controller 2.5 octave and a Behringer UMX-61 Controller keyboard. The Behringer I bought because it links up by USB and needs no external power - nice for a laptop.
My software at this stage is BIAB2006, OMB9, Ntonyx Arranger, Jasmine Orchestrator (VST) which I use along with Cubase SX to produce the starting backing beds for my projects.
I can also produce backing beds with the EXR-7 and PA80 by recording to the onboard sequencers and saving a midi file. Or just recording the audio straight into Cubase.
For a long time I have looked for the definitive software solution to a real-time arranger. OMB comes close in some areas. Control is usually the issue that lets this process down. On hardware arrangers you have buttons to control fill-ins etc but on software up to now you have to press a computer keyboard key or assign a keyboard note to these functions. The latter has it's problems as these are usually assigned outside the playing area and are hard to hit just at the right moment when both hands are busy playing. I have looked at using a wireless keypad and this may work but they would have to be mounted on the keyboard in an area away from other controls and displays - usually meaning again that they are hard to access in the heat of playing. The answer may be in using something like the Behringer FCB1010 midi footpedal, but I need to figure out how to have two midi inputs into OMB.
Maybe the next thing for OMB is VSTi support as that could be awesome for live use. I know you could use a midi yoke or similar but having everything in one central program means saving setups becomes a breeze.