I hate PCs. I'm a Mac user for a reason. But I needed a backup solution for my Mac, and the miserable best I could find was to run Retrospect on a Windoze box. Sure, I could run it on a Mac, but that would mean dedicating a Mac to the boring and mundane task of sitting there all day waiting to back me up. Plus, a Windoze box is much cheaper, and I was able to set up an SATA RAID array to hold my backups.
Okay, so I started putting some other software on my PC. Not much, stuff like the TiVoToGo software that still isn't available for the Mac. Anyway, at one point, after a few weeks of reasonably reliable operation, networking on the PC started to go south. After reboot, it would work fine, but you could watch Retrospect scanning my Mac and see it slow...down...do a crawl. Just a few bytes per second. Nothing like the 100-200 MB transfer rates I was getting before.
After much poking, learning more about PCs than I ever wanted to know, and lucky Googling, I discovered that the on-board nVidia Ethernet hardware has some trouble with power management. So, I disabled that feature in the driver, and now it seems to work fine. Not sure when that feature got activated, or why it was only now giving me trouble, but who cares?
By the way, if you need more evidence as to why PCs suck ass: there are databases on the web explaining the function of various cryptic files you find executing on any Windoze box. In my case, I was trying to determine what piece of software might've been causing problems. There were lots of vague things in the process list, stuff like nSvcIp.exe and nTrayFw.exe. I knew my box had a lot of virus protection crap (wholly unnecessary on a Mac) from nVidia (they make the chipset on the motherboard), so I investigated some of these files. It's amazing how many entries in the DB were for the actual file (maybe one), and how many were for files of similar or same name that were the leavings of various trojan worms (literally dozens). What a piece of shit Windoze is.