I'm looking into creating a class that will gravitate toward an area or mouseX/Y but then be repusled by the same area if mouse is clicked or something similar.

I've seen some nice examples around, but some of the math is a little beyond me (atan, etc).. and I would like the objects to hover around the attracted area somewhat tightly but without stopping altogether.

Help = much thanks

Explinations about atan or links to simple trig sites would be good too

It's probably a lot easier to think of x and y as separate rather than worrying about trigonometry too much. It sounds like you need two attractors (two magnets). When you press the mouse down the other attractor is activated. Below is a simplified code of this. You could copy the x stuff into a y function to get two dimensional movement.

The second magnet is on a timer. Instead of either one being on or the other being off you might want to experiment with either magnet increasing or decreasing in strength (could use more timers and divide by their value).
Code:

Particle [] particle;
int timer = 0;
boolean toMouse = true;
void setup(){
  size (400,400);
  particle = new Particle[20];
  for (int i = 0; i < particle.length; i++)
    particle[i] = new Particle();
}
void draw(){
  background(200,100,50);
  for(int i = 0; i < particle.length; i++){
    particle[i].draw();
    particle[i].drift();
  }
  if(timer == 0)
    toMouse = true;
  else{
    toMouse = false;
    timer--;
  }
}
void mousePressed(){
  timer = 50;
}
class Particle{
  float x,y,attractorX;
  Particle(){
    x = random(width);
    attractorX = random(width);
    y = random(height);
    toMouse = true;
  }
  void drift(){
    float delta = 0.0;
    //decelerate - divide difference
    if(toMouse) delta = (mouseX - x)/16;
    //accelerate - divide difference and subtract from difference
    else delta = (attractorX - x) - ((attractorX - x)/1.5);
    x += delta;
  }
  void draw(){
    ellipse(x,y,10,10);
    rect(attractorX,y,10,10);
  }
}