Computer start up gets slower with every Windows Update!
Yep, Windoze would be my first thought. I've turned off automatic updates for years now. Some people say it's irresponsible and I'm putting the entire internet community at risk but by my reckoning a healthy dose of paranoia and multiple layers of security are probably better than just blindly trusting a faceless corporation to look after me. Not only do things run more slowly after each update but Microsoft also has something of a track record of catastrophically breaking things during an "update", making it particularly difficult to undo it.
I forget if it was Windows 7 or Windows Vista where an automatic update broke the network functionality. Good luck getting the update to fix the previous update, when you can't get online. About the only solution is to use a different computer (you have multiple PCs in the house, right?) to download an update onto a USB stick and transfer it that way. Except it was back in the days when people didn't necessarily have USB sticks lying around idle either. Never mind, you can burn a CD, as long as you have blank CD-Rs kicking around.
Or you can do what I do and turn off updates.