In Blender 2.5.2 when I drop an obstacle in a fluid (example a simple cube dropped in water), the fluid does not reacts at all. If the obstacle is static the fluid goes around as expected.
Apparently moving obstacles were not implemented in earlier versions of Blender but it works in 2.4.9 with which I could make some nice spashing animations.
Could you confirm my impression or explain a new manner of usage. If indeed this does not work I will post a bug report.