I thought I'd post a solution to a problem I had recently - it might help someone else. Last year I was getting 30+ Mbps down with Comcast using their "Boost" option (costs a bit more than regular). Then this year, it dropped to 10Mbps. Of course I complained to Comcast, ran all types of scans, checked my PC with HighjackThis, etc. Nothing. I have a Dell XPS with a mother board capable of handling 24GB of RAM. I had 15GB in it but then took out a 1GB stick to put in a 4GB stick giving me 18GB of RAM. I also have a bootable second hard drive "F" with Win 7 Ultimate but my primary "C" dive has Win 7 Home Premium.
The puzzler is the secondary "F" drive was still getting more than 30Mbps down but the primary "C" drive was only getting 10 Mbps. What's up with that? I tried everything until I discovered that Windows 7 Home Premium can only "handle" a maximum 16GB of RAM - Win 7 Ultimate can "handle" 192GB of RAM. When I dropped my RAM back to 16GB my speeds returned to above 30Mbps on the primary C drive.
The lesson for me is that if you put more RAM in your machine than your Operating System can handle, you might down grade your speed when you think you're helping.