A whole lot of fun and a bit of aggravation too!
(the following is a direct lift of a post I did on TwoPeas a few days ago)
Our little Simba is not so little anymore!! Since his arrive in mid-June, he has tripled in size. He was neutered on July 11th and come through with flying colors.
He is by far the funniest and most affectionate cat I have ever met. He loves to be cuddled and will lay in your arms like a baby or like a rag doll. When he's not in your arms, he's jumping around in silly fashion. Alternately attacking piles of hay I put out for the horses, flying bugs, an empty feed bag or one the toys we've bought him. He thinks the tack room where we have hay stored is his personal playground. So many things to attack, places to climb and jump from, not to mention great hiding places.
By far though, his favorite past time is annoying our dachshund. Once he realized that the dogs can only go so far (constrained by the invisible fencing we have), he has come to delight in sitting *just* outside of her reach. I happen to place a "camp chair" just outside of this zone and he has come to consider this his very own thrown. He climbs and plays on it or just lounges as the dog sits mere inches away, going mad at the sight of him.
Today, I heard the usual mad barking from the dog and went out to tell her to knock it off. This is what I found:

At first I thought Simba was "trapped"...when I got closer (with the camera I had gone back inside to get), I discovered that he was actually a picture of relaxation. My guess is that he purposely went up the tree in his on-going plan to drive the dog totally and completely out of her mind.

This brush is a favorite toy. He was so focused on playing with the brush that he nearly fell out of the tree a couple of times.
And here's a closeup of the poor dog who has met her match in feline form. I couldn't have come up with a better exercise program for her...she will spend hours running back and forth in front of the fenced area where Simba rules.