Everybody's getting their panties in a wad over this lame legislation, so I'm going to take a counterstance.
Poker Transactions
Online poker transactions will largely be the same for anyone who uses Neteller or a similar service. Naysayers will point to the wording about "intermediaries" , but it's largely lame and easily worked around.
How so? Think of something similar to Neteller's InstaCash (but without the "fvck you fees"). I'll have two "accounts": one at an online wallet service that does not deal with poker companies, and one that does. I'll one-click (a la Fast Cash) at my online poker wallet (OPW) to say that I want $1000 in my account that I can use to send to Stars, Party, or whatever. They make an automated request via my non-poker related online wallet that then requests the money from my bank. My bank will not have to refuse the request to the non-poker related online wallet, and the US government cannot realistically regulate whether on offshore intermediary works with another offshore intermediary as long the initial transaction cannot be traced to a company that primarily works with online gambling. The non-poker related online wallet then sends it to my OPW. It sounds like a pain, but the only extra effort most of us will see is when we have to set up accounts at two sites. Other than that, it'll still be one-click cash.
The caveat to this method is that the initial intermediary needs to have a very diverse range of transactions (i.e., not primarily poker- and gambling-related). Neteller will still probably remain the online wallet of choice, but Neteller or some other company needs to come up with a cushion company between themselves and US banks that looks more like PayPal than Neteller. This may take a year or so to establish.
US Residents
I seriously doubt that Party and Stars will ban US residents from playing -- it's too much of a cash-cow and the legislation largely does not address the poker sites themselves. Yes, the primaries of these companies will have to avoid the US and countries with extradition treaties with the US, but I imagine these people will gladly pay this (temporary?) price given that it will likely mean billions for their companies and millions for themselves.
If somehow one or both of these companies ban US-based players from their sites, don't be surprised if they unban them once things settle down (i.e., 3-6 months).
The Legislation
I think this is going to be really hard to enforce, and I imagine the regulators assigned to making the enforcment rules are going to try to find a way to dodge the tough work. One possible method to do this is simply to wait until the new Congress comes in and then pressure them to repeal or alter this Act. Another way is to interpret the wording of the Act in a weak way so that it essentially has no teeth (e.g, avoiding tracking offshore intermediaries actions with blacklisted offshore intermediaries like Neteller).
The WTO will also make this Act a tough sell. Expect lawsuits and other various legal challenges. Of course, the US has shown no inhibitions in ignoring the WTO in the past, but it's never fun having your faced rubbed in shitty regulation that passes via 11th-hour chicanery. I think the WTO angle will heavily influence the regulators who are in charge of making up the methods of enforcement.
Finally, I think the UK will come to the rescue in two ways. First, they will be backing up the WTO -- or at least not backing the US. Second, they will show that regulating and taxing online gaming is a FAR superior option than this ridiculous crap we're currently sitting on.
Expect this legislation to be repealed or substantially altered if/when the Democrats have more power in Congress and (perhaps) the executive branch. Expect regulated online gaming in the US within the next 5 to 10 years.
The Worst-Case Future of Poker
If Party AND Stars pull out of the US market AND don't re-enter, then it will take a while for online poker to stabilize. These two sites have a big player base and have done a lot to build their brands to the point that they can attract the fishies in droves. It will take a while (a year or two?) for another site to gain the kind of status and reputation that Party and Stars currently have. If the situation pans out this way, I imagine the growth of the site or sites that take the place of Party and Stars will be seen as the rebirth of online poker.
Even in this worst-case-scenario, online poker will continue to flourish -- although on a smaller scale for a while. I think the Asian market is going to be HUGE, and I think the European market has a lot of room for growth. At some point, US players will flock to online poker sites again (after next year's WSOP ME appears on TV?), and I imagine they will find the situation as good as or better than they left it.
Relax, play some poker, and make some money -- the world's not coming to an end.