It will likely make no difference for most applications -  few are enabled for multiprocessor support.

 

You will be able to run more than one app at one time (if you have enough RAM)

It allows more program to be going down the from side bus by filling in the extra gaps that are not being used by the front side bus.

As you see, it is easy to change. Try it both ways and see which works better for you. In my case, some of my most processor resource intensive programs run about 10-20% faster with HT enabled. And there is also a speedup if you run two processor intensive applications simultaneously. You can look at the Task Manager to see if you are getting any benefit.