http://www.nhc.noaa.gov/refresh/graphics_at4+shtml/091832.shtml?prob?large

Based on that, and the size of this storm and its projected intensity of landfall, I'd secure your supplies and board up. An evacuation order isn't going to come until this evening at the soonest and your preparations should already be made.

Don't wait too long and be one of the folks scrounging around for plywood 24 hours out. That was me with Frances last year. Fortunately, Frances was a slow-moving storm that gave me enough time to get 4x8 3/4" board that friends and family had extra after doing their own houses. I ended up with just enough to spare and was even able to help an older woman across the street board up her front with the leftover sheet.

My new house came with hurricane ply, and my wife and I have our hurricane stores already set for the season.

I guess my point is this. the NHC has Dennis heading your way as do most of the models. It is prudent to take whatever steps you can. It's a lot easier to unboard a house after the storm misses, than it is to ride out a Cat 2+ without any protective measures. You certainly don't want to be boarding up while the rain and wind are picking up - that can get plain nasty.