I personally haven't noticed any BMAX specific problems with smoothness, other than 1ms resolution timer, but that doesn't really make a difference. 2D games are generally harder to make appear 'smooth' because side scrolling usually happens at a universal magnitude, so any hichups are noticible right away.
Also, DX and OGL rendering happen at subpixel precision - but some monitors (like LCDs) have very pronounced pixels, so transition of a polygon between a single pixel might appear like it's jumping from one pixel to the next (like no subpixel accuracy), but if you pay close attention to the texture inside the polygon, it will glide smoothly from one pixel to the next. Subpixel precision is done with texture filtering (OGL&DX), and specific monitors will show much edgier transition of polys from pixel to pixel. Defringing your sprites, adding alpha blended edge smoothing to textures, and setting proper texture wrapping modes (clamping) helps tremendously with this discrepansy.
Also, DX and OGL rendering happen at subpixel precision - but some monitors (like LCDs) have very pronounced pixels, so transition of a polygon between a single pixel might appear like it's jumping from one pixel to the next (like no subpixel accuracy), but if you pay close attention to the texture inside the polygon, it will glide smoothly from one pixel to the next. Subpixel precision is done with texture filtering (OGL&DX), and specific monitors will show much edgier transition of polys from pixel to pixel. Defringing your sprites, adding alpha blended edge smoothing to textures, and setting proper texture wrapping modes (clamping) helps tremendously with this discrepansy.