Yeah twixtor is the way to go if you want (For 1.5 version) real slow motion keyframing, but it's way too painless because it requires rendering and you have to create nested sequences which tend to crash once in a while, overall I just don't like it.
The way I use to create the "ease out" effect is to cut the final portion of the clips into small pieces, each with a different clip speed in 10% or smaller increments depending on my needs and the length of the clip.
Maybe PP2 has clip speed keyframes, has anyone checked on this?