There is a sizable group of ACT! users that happen to be Thunderbird users as well. In terms of complaints, this appears to be one of the big things ACT! users continue to talk about.

All we want is an alternative to ACT! mail and Outlook.

Let me put it this way:

Your great aunt and uncle are coming into town from Connecticut. Because you are their favorite grand-nephew they decide to take you out to dinner at a restaurant that is renown for only serving clams.

But you're allergic to clams.

You can't very well leave the restaurant. Your great aunt and uncle would hate you for it and the maitre d is a bipolar ex-guerrilla from Guatemala who happens to be carrying a 9mm on his person, and would be VERY insulted if you walked out the door. 

You don't want those clams because you know that eventually you will swell up like a balloon and suffocate to death or begin convulsing in anaphylactic shock. A bead of sweat drips down your forehead and you feel hot from the mounting pressure.

That settles it. It's time to do something drastic...

You leap out of your seat and grab the nearest chair out from under another patron's bottom and hurl it through the nearest window.

Before defenestrating yourself, you grab a fistful of silver dinner knives and tiny crab forks in case the maitre-d has enough time to realize what is going on and draw his gun. You fling what you have, as you hurl through the shattered window, at the maitre-d, a knife striking him square in the forehead.

Go. Run! The sous-chef is brandishing a ladle and oregano, shouting angrily.

Your only hope of survival is to find a method of transportation. Audi... locked. BMW... too James Bond. Then you see it: The Unicycle. It can outperform any vehicle in its one-wheeled handling. It is literally capable of stopping and turning on a dime, not like those huge boats other people claim are cars. The chrome of the fork shines in the street lamp lit night.

So, you see, it is important to have options when using software. People have preferences that others might not consider options in the first place because they're so limited with their initial choices.

Give us what we want.

Don't make us eat clams.

Give us Thunderbird.