Does youtube cause my hard drive to fill up quickly?

I just switched to cable internet last month from dialup (yes, I waited a long time). In that time, I've discovered the wonderful world of Youtube, but in that time, also, my hard drive managed to fill up very rapidly, by about sixteen gigabytes, by my estimate. It's completely full, now. I've had to delete my entire music library just to function. The only things that have changed during the time of rapid filling were my new broadband connection and my use of Youtube. That's it. I don't download the videos. I only stream them. I did a search of all files, visible and hidden, that were modified or created in the last month, but I can't find any likely culprits. The My Documents section was unaffected. The Windows section grew a couple of gigabytes, but the Program Files did most of the growing in that time. No particular sub-folder in Program Files seems to be responsible, and the total space used by individual folders doesn't add up to the total space used by Program Files, even with hidden files included. I couldn't find a virus, either. What happened, and what can I do to avoid it in the future?