Upgrading is NOT an option on the psr2000. It was advertised with the intent of a flash system, but delivered without it.
For most users, the o/s bugs are of little importance. I have only one real gripe with the unit, and that is construction. It's cheap, flimsy and feels terible. (OK, three gripes)
As far as sounds, styles, and mic effects - it's the best bargain out there in a mid-level home keyboard. It falls short of the next level on many points, but it makes some terrific music, if your needs are simple and your touch is light.