As many of you are aware, you can use your digital piano/synth/midi controller to send MIDI signals to an external tone generator/sample player including computer based soft synths and samplers.
With dedicated tone generators and hardware samplers, things generally just work, but for software based instruments, many problems can be encountered. One of the more common issues is latency (the time from when you push the key on your controller to when you actually ear the sound from your speakers). There are many causes of latency (computer CPU performance, application performance, application interruption, OS configuration, disk speed, etc.) but one of the first places to look is at the overhead imposed by your computer's MIDI interface (hardware and drivers).
I just found a tool that appears to measure this overhead and will give indications if the latency problem you are encountering is related to you computer MIDI hardware. It's called (surprise) MIDITEST: http://earthvegaconnection.com/evc/products/miditest/index.html
I haven't had a chance to try it out yet but I thought some of you might be interested.
Hope someone finds this useful!