Is it legal to use a company's name within a URL, to point to a site that sells nothing and has no ads, but describes their product and has a referral link?
If is not a trademark you may use it ..if is trademark you have to ask for their permission. I've seen a lot of Adsensesecret , adsensegoldmine etc etc sites and they do just fine
as MSM said, if it is not a trademarked name, you **might** be okay. Even if it is not a trademark, if the company is well known, long established, and has a widely established base, they may still petition for removal of your use of the name in court, or lodge a WIPO / ICANN-UDRP dispute. Some companies pursue this option vigorously, other do not bother about it. You can never tell which ones will, and which ones will not. If the domain name is a trademarked name it may well affect any affiliate associations or even google adwords etc. if you use that domain name in any of the applications or adverts etc.
Keep wondering about the rule. If you register "ABC" as your brand name, thats mean nobody can't use it for commercial use? Including for domain too? Looks like it's not fair.
No, it really depends on what are you really doing with the domain PayPal.com PayPalsucks.com PayPal guys every sued sucks.com? no, simple reason, they don't have to do anything with them, its like a blogging site where users post their comments about PayPal. But if it were a payments processor, PayPal would have surely asked them to change the domain name since it infringed their copyrights. The main reason is there are more infringes than anyone can handle and no one wants to spend lots of on just legal cases, fees etc. even if its not related to their business?0