A few helpful (I hope) bits.

Disclaimer- I did my law degree about 15 years ago, and am not a practising lawyer. Please don't take anything as concrete, and always seek professional legal advice in important matters.

Ok, first up- copyright applies to works, not ideas. Any idea that anyone has can be ripped-off, but once those ideas have been expressed in a certain way, that form is protected. So Superman's power-set is an idea, and not protected, but the presented form (hairstyle, costume, name, friends, and so on) cannot be used without permission. So, although Superman cannot be used without DC's permission, a character who is very similar to Superman can be created and used, even as an obvious stand-in for Superman, such as Supreme, Apollo (Wildstorm), the Sentry, Gladiator from the Shi'ar Royal Guard (technically a copy of Superboy, for all the difference that makes (see below)), Hyperion, and more.

Trademark law applies to names, slogans, catchphrases, and so on. This is applies (in theory) only to covers, posters, advertising, and so on, but not to the bulk of a work. The protection of trademarks is not connected to copyright law. This can be seen in the case of Captain Marvel, where the trademark on the name expired, so Marvel Comics decided that they would register it. DC were free to keep using the original Captain Marvel character, and still call him Captain Marvel within the pages of the comics, but they couldn't call him that on the covers. It's also why Dynamite make comics about Tarzan and John Carter, but can't use the names of the characters on the covers, and why the original Daredevil gets renamed so often.

However, it should be noted that there is no clear line to cross (or stop short of!), as the law will be interpreted by judges, who might decide things differently. The original judgement in Fox's Wonder Man case would probably be decided differently today, as the character doesn't seem to be very similar to Superman at all. The legal issues around Superboy were strange too- literally just a younger version of Superman, but considered to be a separate character.

Always remember though, it's no good to be right if the other guy has a lot more money than you! Unfortunately, if you can't afford to pay for all of your legal costs, you can be bullied into backing down when you're in the right. It absolutely sucks, but it's reality. This is why, for example, Dynamite call the original Blue Beetle "Big Blue", as well as renaming other characters.

Check out these links for more examples of writers (almost) using other characters legally:

http://tvtropes.org/pmwiki/pmwiki.php/Main/CaptainErsatz
http://tvtropes.org/pmwiki/pmwiki.php/Main/LawyerFriendlyCameo
http://tvtropes.org/pmwiki/pmwiki.php/Main/WritingAroundTrademarks

Didn't realize you had a legal background, Whizz! From hanging out here and other spots on the 'Net, I've picked up a little bit here and there, but with ZERO professional legal training!

I appreciate you spelling it out so succinctly. This is pretty much what my understanding was, but it's nice to have it confirmed.

I think what's confusing/annoying to most folks (myself included) is the difference between the copyright & the trademark, because quite often (especially when dealing with comics) the two become merged in the mind of the public. If I'm going to do a new comic featuring the classic PD Daredevil (which I can) and I call him Daredevil within the book (which I can), I damn well want to put "Daredevil" on the cover of the book (which I can't!).

One thing that occurs to me as a possible solution would be to remember that no matter what we're used to in the modern comic industry, in the Golden Age where most of these characters were spawned, the comics were NOT (at least initially) named after the characters. Blue Beetle started out in "Mystery Men Comics." Daredevil started out in "Silver Streak Comics." Heck even the summer's blockbuster hit, Ant-Man, started of in "Tales to Astonish." Perhaps reviving these characters might mean reviving these titles, too?

Yeah, it's all a maze of grey areas, unfortunately. I guess that keeps lawyers in business? Yeah, the fact that the name of a character and the character itself can be owned (or not) separately is a big mind-screw.

Also, I forgot to mention- just because someone claims to own the copyright doesn't necessarily mean that they do. But like I said before, money often counts more than genuine legal claim. I know that some of the characters that should be PD are contested.

Also, copyright and trademarks are different in different countries. Generally, just because the countries have different expiration periods, or don't recognise registration in a different jurisdiction. This is why there are often bands from the UK and the US with the same name, but when one wants to go to the other's country, or release music there, they need to alter their name. Most decent-sized modern publishers will probably have this covered, but it's worth noting. Also, Peter Pan is a special case, as a law was passed in the UK stating that the copyright belongs to Great Ormond Street hospital, and never expires- but this only applies to the UK.

Yeah, I knew there was SOMETHING funky about Peter Pan, but wasn't quite sure what the deal was. But really you'd have to be some kind of a lowlife to try to steal the proceeds of a copyright owned by a children's hospital!

And I totally agree with you about money and people claiming to own a copyright. All the evidence says that Captain Marvel is in the public domain, but anyone who decides to take DC/Warner Bros. to court over that issue needs to have their head examined.