your frames get blurry if you choose to blend them together, or motion gets choppy if you dont. there are newer interpolation methods out there but i did not test them. Either way youre better off shooting at the fps you want.
Cineform Neoscene will not convert anything unless it is a 60i footage (59.97). In all other cases it conforms (it has some pitch adjustment though). Please search the forum. There was a recent discussion on frame rate conversion.
This technology tracks each pixel on the screen and figures out the exact motion in the pictures. It can then be used to create new frames between the existing frames. The most common use for this is to synthesize slow motion from normally shot footage.
Many editing and compositing programs now have optical flow retiming features. Motion and FCP from Apple have a very powerful retiming solution, originally developed for Shake.
Retiming from 30 to 25 or 24p requires the software to create new frames in the new timebase from the old frames. In other words, it looks at samples taken 1/30 of a second apart, and creates new frames between them and discards the original frames. Artifacts can occur using optical flow. You should experiment to see if it's acceptable to you.
The best solution to get a cinematic look in 24 or 25fps is to shoot at that frame rate. There are many inexpensive cameras that shoot at these rates.