We all have war stories about this but Fred Langa just wrote a great post on how bad it gets. You can read the post here.
While the goal of the post is to test Registry/system cleanup tools, the part I find most amazing is how much the crapware he used to test with slowed down the system.
In a nutshell he created a minimalist Windows XP image. Then he installed the software from "CNET’s list of the '20 most popular Windows downloads.'" While he links to that list, after reading his results I won't even link to that list.
I installed all 20 apps on the test system as inexperienced Windows users might over time - layering on the software without regard to consequence and accepting all default settings, including the offers of extra toolbars, download managers, and so on.The results were incredible. The boot time went from 30 seconds to 629 seconds, over 10 minutes!
The good news is that when he uninstalled those packages the system pretty well came back. Boot times were still slower but nothing like 10 minutes.
You can read the article yourself to see what he found with the Registry/system cleanup tools but I just wanted to share with you his experiences with crapware.