I have a Pinnacle HD Stick and EyeTV 3.0 running on a 1st gen BlackBook w/ 2GB ram. I tune in over the air digital TV with it and have no problems. You will want to do some research about where you are located in relation to the broadcast towers for your local TV stations if you plan on watching over the air digital TV, and get an appropriate antenna. I have a Channel Master 4220 2-bay antenna mounted in my closet, and a Channel Master 7775 Amplifier. I can tune in 11 stations (plus all their sub-stations) with this setup. With the small antenna that my tuner came with I only got 5, 3 of which were Spanish language stations.
While watching TV (including HD broadcasts) I have had iTunes downloading new purchases in the background and surfed the web in Safari, without any problems. The only thing I could not do was have my HD tuner and an analog tuner connected to USB at the same time. I have an EyeTV EZ analog tuner that I used to use. If I plug them both in, I get an error that the USB bus can't handle them both at the same time, which is a shame since EyeTV supports dual inputs.