Are you talking about latency or jitter?

Does it sound OK if you later play back the recorded MIDI data through the PSR?

Thanks for responding.
The live sound as I'm playing has the same delay as the playback, if that helps clarify. For instance, a 3-note chord sounds fine live while recording, and plays back fine after. However, a faster progression has a delay between the key down and it showing up in the DAW and playing over the speaker, and it remains delayed on playback. It's like the notes are getting bunched up as they're inputted.
Would it help to play back the MIDI through the keyboard? It's harder to tell if it's delayed that way, because I have acoustic instrumentation in the DAW project that are mostly driving the music I'm recording the MIDI to.

What you're describing sounds like a latency problem within the MIDI to USB convertor.
This is a very common symptom found in the very lowest cost MIDI/USB interfaces.
It's usually solved by buying a quality product from a well known producer of equipment.

Colin, to find out which component is responsible, could you try recording MIDI on some other PC, or with some other MIDI sequencer?

So I had wanted a real controller anyway, because I want to be able to do some pitch shifts on at least one of the tracks and the Yamaha PoS doesn't have that, so I just bought one for $90. And that seems to have improved it greatly. Ardour recognizes the controller and I'm not seeing latency issues at all.
Thanks for the help though!