Greg,
Like any soft compound racing tire, you'll have to heat cycle them, not only for traction but for longevity. An often-made mistake is to heat up the tires but not allowing them enough time to "relax". This must be done for a minimum of 24 hrs after the initial scrubbing or heat cycling of the set. Many folks will waste a good set and be unhappy with subsequent performance because they didn't want to waste the track time. A way around this of course is to scrub the tires, take them off, put on another set. Usually with new tires, you really waste the first day heat cycling your tires. It's worth it though, better than having squirelly tires for the rest of the season.
A summary and easy on-street alternative: (direct quote from tirecradle.com)
Heat Cycling (breaking in) New Tires
New tires are expensive and new performance tires are very expensive. As such, we thought that we would mention the correct way to ‘heat cycle’ your tires for both longer life and, more importantly, better traction over the lifetime of your tires.
When you buy new tires you should heat cycle them to insure long life and optimum traction. Heat cycling is quite simple and is imperative for performance tires but few have heard of this process yet alone know how to do it.
To heat cycle your tires you should do the following: Drive your car at about 55 to 65 mph for about 10 miles. Then drive the car slowly to let the tires cool for about 2 or 3 miles. At this point the car should be parked and the tires should be allowed to fully cool uniformly. Uniform cooling will require you to either jack the car up off of the ground or to use Tirecradles. If you cannot jack the car up off of the ground and if you do not have Tirecradles, then try to park the car on grass. The thing that you do not want to do is to park the car on concrete as this may cause a ‘cold set’ to occur at the site of the contact patch. This will result in a spot that will always be a little harder than the rest of the tire. All tires have a certain number of ‘heat cycles’ in their life; that is, before they become hard. Correctly heat cycling your tires the first time will greatly extend the useful life of your tires.
Having said this there is one caveat; heat cycling can only be effectively done in non-winter months in order for the tires to build the necessary heat. As such, try to avoid buying new tires in the winter.
Here's a good read:
http://www.porschenet.com/bfgtires.html
Note they all say you MUST let the tires relax off the car. Like any workout regimen, the most important part of the strength-building process is the rest period...