Steam registration took a long time for me on my 56k dialup. It should be noted that I installed two days after HL2 was released so server traffic was probably kinda high, but it took several hours for it to finish unlocking the files for the game. Fortunately I was lucky enough to get the offline mode to work so it didn't have to log into the Steam servers everytime I wanted to play singleplayer, but Steam itself started up whenever I used HL2, and combined with the loading time for the levels and the main menu, it took a while to get from clicking the executable to actually playing the game.