Here's another 'Assemble' Effect...this time some Text coming together. Now, to control how fast they move and how fast they appear, you adjust the FCurve. We are using the TimeInState to determine how long the particle has been in a particular state or 'activated', and then using an FCurve to calculate the ratio between how long the particle has been in a state and a value range of [0..1].
A FCurve is modulating between the particles current position and it's EmitPosition [where it was born] and another FCurve is modulating the particle scale [its the only way I could figure out how to hide polygons].
This file also uses the newer versions of the compounds [Init Polygon Particle & Anim Polygon Particle], just to explain it a little, Anim Polygon Particles: You can select which Particle data you want applied to the Polygons. Since retrieving and applying this data has a cost [in terms of time], then it allows you to gain some speedup if you dont need Pos & Scale & Rotation. If you just want Position, then you dont have to waste time getting Scale/Rotation as well.
Here's the file: Logo Motion