Particle Motion Transfer to Scene Objects - The following simple tutorial shows the basics of moving Max scene objects using PF particles.
This method can be applied to lights, helpers, geometry objects etc.

Scripting Custom Chunks - The Basics - The following simple tutorial shows the basics of creating custom chunky explosions.

The Hairy Teapot - The following very simple tutorial is exceptional as it does not feature any scripting at all.
Someone asked on a chat forum about aligning objects to the surface of the emitter...

Inherit Texel Color From Emitter - This technique lets you assign the color of the texel at the Emitter's surface to the particle born at that point.
While it is considered a "hack", it can be useful.

Particle Resolution By Camera Distance - This scripted approach is a further development of the example found in the MAXScript Online Help.
This version can be used with arbitrary mesh as particle shape. 
To achieve this, the Particle Flow Script Operator controls the optimization values of a MultiRes modifier!

 

Length By Velocity - Particle Flow has the ability to display particles in the viewports in multiple ways, including lines representing the velocity vector.
Unfortunately, there is no comparable mode to render geometry particles for the final animation.
The following tutorial assigns a box to the particle shape and changes its height based on the particle's speed to achieve a similar effect.

 

Force By Mass - Particle Flow allows the user to control the influence of certain Force-related Operators via MAXScript-generated particle channels. 
This is called Script Wiring and is a rather hidden option. 
The following tutorial shows how to calculate a mass value for each particle and control the influence of a Wind force to get a more realistic behavior where light particles are blown away while heavy ones stay almost unaffected.

Ride The Flow! - This tutorial shows how to create a Camera Ride on a Particle Flow system.
A Script Operator assigns the transformation of a particle to a scene camera which then travels with the particles in the middle of the stream.

 

Speed By Age - This tutorial shows how to control the Speed of particles based on their Age and LifeSpan using a Script Operator.
It also demonstrates the need for a Delete Operator when accessing LifeSpan values, and a possible way to orient particles to the Source.

FreezePFlow - Snapshot As Mesh - This MacroScript lets you create a Mesh Snapshot of a Particle Flow particle system.
In 3ds max 5.1, neither Mesher Compound Object nor Snapshot Utility can create an Editable Mesh copy of a Particle Flow system.

An Industry Lesson

Animated Water/Sea

Automated Tank Tracks in 3ds max 6

Compositing: Camera Matching

Creating a Realistic Animated Cable/Rope/Flex

Creating Animated Grass

Creating Fire in 3DSMAX

Link Object to a Vertex

Muscle Bulging Using Muscle Bones in 3ds max

Texture based particle emission

The Claw (Expressions)

"Smokin 3" - Advanced 3dsmax Particles