cool effect, but i doubt it was a single effect that did it...
you can probably use ae's text animation properties to create the movement -- there may be an animation preset that is close. once you have the movement, then you could duplicate the text layer and replace the text with a circular character from a dingbat-like font.
now that you have two layers with the same movement, you can use a dissolve between them and an adjustment layer with blur over the top of them to hide/smooth the transition.
note, if the movement was created using a random/wiggle exprression, you'll probably need to set both layers to have the same random seed to keep the positions the same, or render and import each to create the composite.
if you can't get the text animation properties to work for you, you can probably 'manually' create a similar effect...
you can create a pretty good morph by converting the text to shape/mask. then add a keyframe for each letter's mask path. create a circle mask,select it's mask path and copy it. go back to your path text layer, add an new key frame for a letter's mask path and paste the circle path in it. do this for each layer and you'll have a morph from circle to letter for each letter.
to get them to move, you need to get each path onto a separate layer (i'm pretty sure crgreen.com has a script for this, or you could copy/paste).
then you can add a keyframe for the end positions of all the layers, go to the beginning of the comp and randomly spread them about.
add a null layer and add and expression slider control to the null. keyframe a value change on the slider to go from around 100 to 0 timed with the animation of the positions.
add an expression to the position of one of the letter layers and type a = ,the use the expression pick whip to pick the value of the slider, then type a ;. hit return for a new line and type wiggle(a,1) and click out of the expression.
your expression should look something like this (i don't have ae here to check the syntax, but i think this is close):
a = thisComp.layer("null 1").effect("Slider control").slider;
once you have one expression you can choose edit>copy expression only and paste it onto the others.
now the layers should start as circles, moving in a somewhat random way as they come together and morph into letters. add blur to an adjustment layer and do some tweaking.