Routers need to maintain what's called a NAT table as it translates your private IP address on your LAN (e.g. 192.168.2.10) to the Internet routable IP address belonging to your PPPoE session.
When you start something like a bittorrent client, it opens up many connections per torrent: so if you have 3 active torrents you could have 900 open connections if you have the maximum connections per torrent set to 300.
Most routers balk at that level of traffic but custom firmware such as Tomato and DD-WRT, Open-WRT, support many more connections than the default firmware (DD-WRT supports 4096 connections out of the box).
Buy yourself a router that supports custom DD-WRT or Tomato, and you'll notice a difference... plus, you'll be able to manage congestion and use QoS to prioritize your traffic so that your Skype traffic has priority over your http or bittorrent traffic thereby helping minimize freezing and distortion.
@HeadSpinning, Ok, so that means the router needs to be restarted once in a while. It hadn't been turned off for many months.
But on Monday I did restart both the router and the modem, and didn't seem to have any effect. It was only after I removed the router and then put it back in service that there was any change in speed.
But good to know, next time I'll have something to test.
@Nat, No torrents here, but definitely will follow your suggestion to get a better one next time. Currently it's just a plain WRT54g. It's been solid for 5-6 years now, but heavily used.... maybe its time has come.
Remember the squeals that used to be heard from a 56k modem (eeeee EEEEEE shh shh boing boing)? That is called training, the modem doing various modulation schemes to get max speeds going. Your DSL modem does the same wo/speaker. Storms, noisy phone lines etc can cause your DSL to drop in speed. The power cycle (off/on) is what brought the speed back. The router has nothing to do with it. Bell throttles all non Bell customers. We had about 5MB, they dropped it to 1.5MB. But for that we have true unlimited w/Primus.