I pre-loaded mine about a week ago with no problems. Steam downloaded about 4.3GB of data in roughly in hour. What kind of connection do you have? And are you behind a firewall?
I'm on a cable modem at home with a firewall/router and I have several ports open specifically for Steam. Maybe opening some ports will help?
On a side note, I wonder how many people bought HL2 in general, and how many of those purchases were via Steam. Personally, I had no problems whatsoever and will buy from them again.
Half Life 2 is amazing...