Answers to some of the questions above
I will try to answer some of the questions that have popped up during this thread.
There is no "hard" limit to the number of amicus briefs that can be filed. As a practical matter, the briefs are self-limiting. The briefs are extraordinarily expensive to produce, printing costs will run $2,000 alone, as they must be professionally bound, are on weird size paper, have to have certain color covers blah blah. So the number of people doing it "just because" face the initial threshold of cost. Figure at least 80-120 hours legal work plus the costs of printing.
I strongly suspect you will see more than 20 come COB monday.
Another limitation is just the arguments that can be made. Amicus gets 9,000 words, merits briefs get 15,000. That includes footnotes. How many different ways can the same case be argued? That is also why some briefs make almost mention of "what the second amendment means." More on that later.
As to consent, the court freely grants motions to allow amicus to file. Thus, the practice of most counsel is to file a letter with the court saying "we consent to all people who give us notice" filing briefs. At the SCOTUS, the main parties have little control over who files in their case. If someone completely disagrees with the way plainitff is arguing the case, in most instances that person can file an amicus brief saying "we agree with the result but plaintiffs are a bunch of goobers."
The statement of interest and histories of the groups. Technically, only groups with an interest are supposed to file the briefs. Thus the SCOTUS rules require a statement of interest. That is why those resume statements are in each brief.
(assuming we win) The effect of the Heller decision will be limited to the three D.C. statutes before the court. They will not, for instance, strick down chicago in their decision. But the decision can and will be used to stick a sharp stick in the eye of these places in the immediate aftermath. That is the way things work, folks. Building blocks. Look at the civil rights cases. They started with rock solid but very narrow decisions, which were built on. Answer the fundamental question, does it mean what it says. Next answer whether the amendment applies to the states (incorporation.) Next answer the standard of review (strict scrutiny or the DOJ suggested sister-kiss standard etc. As for the specific questions on the machine gun laws. Ultimately, I don't think it will overturn the machinegun framework in place, but what it might very well do is reopen the registry, rulling that capping the introduction of new guns into the registry is violative. That, afterall, is what DC's law does. Requires registration, but doesn't provide for registering any new guns. Just my three cents. (I get an extra penny because I signed a brief.)
The arguments made. It is completely a waste to have 20 briefs argue "what part of 'shall not be infringed' don't you understand." WE all know what it means. The parties are going to argue about what it means. Several amici will argue what it means. several amici will argue the history part of it. Several amici will argue the linguistics. Several will argue criminology etc. Nothing screams assclown like a giant "me too" brief. Thus the trick is to get each amici to address a particular need without duplication. I think you are getting a great demonstration of that nimble drafting in this case. Some duplication, but very little. And where it does exist, it exists with a purpose. For instance, the congressional brief might be duplicative, but it serves the purpose of adding "prestige" parties to the side. The upcoming state AG brief by ted cruz likewise will rebut the anti's state ag brief, even though the arguments are slightly duplicative. The upcoming state prosecutors brief by maricopa county, AZ again balances the anti's brief, even if somewhat duplicative.
So, read no brief in isolation; rather, read it as a part of the mosaic. If, for instance, you look at our Buckeye brief (commonly referred to as a Brandeis type brief) you see lots of emperical evidence but little legal argument, but then flip to page 31 of the SAF brief and they argue about the legal right to self defense. JFPO talks about genocide, PP talks about special discrimination and hints at the need for protection from class-based discrimination etc. Maybe one particular justice likes one particular argument and one paritcular brief will target that argument for that particular justice.
It is all out there; most of it wonderfully interlocking and serving a purpose. History in the making. Sit back, read them all, and enjoy the close to or more than $1,000,000 in legal work product filed in support of the Second amendment.
I hope all this helps. This is one of the more intelligent threads going and i wanted to chime in to help folks out where possible.