What are common causes for greatly decreased internet speeds?

It might be irrelevant, but are the Windows download speeds after using a download accelerator? I think windows did not report its download speeds for updates.

In case you are wondering why the software center downloads are slow, it might be because it uses wget (which does not use an accelerator) and is like downloading files using plain firefox.

Try installing axel, apt-fast and see if that might help :

sudo apt-get install axel
sudo add-apt-repository ppa:tldm217/tahutek.net
sudo apt-get update
sudo apt-get install apt-fast

And then use apt-fast instead of apt-get for eg. sudo apt-fast upgrade or apt-fast update.

I cannot speak about any other reasons for slow speeds on Ubuntu, and am pretty sure that I've gotten better download speeds in Ubuntu than ever in Windows. Try taking a look at your network usage in gnome-system-monitor and see your network usage. Also since you are on a wireless network, try updating your network drivers.

My guess it's a driver discrepancy between Windows / Ubuntu. Also a guess is Bufferbloat.

Give this line a shot and see if anything changes:

sudo ifconfig eth0 txqueuelen 0

This tends to fix the issue of latency under heavy load - not so much raw download speed, but you may notice some improvement.

If you want increased speed downloading 11.10, use a torrent program like 'transmission' or BitTorent. You will get the data from multiple places (simultaneously) and your download bandwidth will be used to the max (or whatever max download speed you set).

I also tried http://www.jonboy60.com/2011/11/02/how-to-increase-internet-speed-in-ubuntu/

I could take out the code if it didn't work anyways. I just applied the settings a few minutes ago; it seems to have sped up my connection.

Nice tip! I'm using Ubuntu 11.10. I'd recommend for anyone who has a crappy DSL connection to try it. If it doesn't work for you, just remove the extra code.

Cheers!

*After testing for a few hours* Okay. I did a laptop to laptop comparison. My laptop against my wife's laptop -- both on Ubuntu 11.10 -- mine, with the tweak; hers, without -- ran both laptops on speedtest.net.

And the results are... they have the same internet speed, which is why I am going to go against my earlier comment.

What seems to have happened was that my ISP was erratic at the time of testing after I first added the code, and the spike I witnessed was probably a fluke.

I'm taking the extra code out.

Peace!