This thread is for webclient developers--or any who are just wondering about it--to fire away with any questions they might have. Your feedback could be very helpful to improving the documentation, and might even merit a FAQ section.
I'll get the ball rolling with questions I've seen a lot here, and will update as new ones come in. Eventually I can add this to the doc. Also if you've seen a question repeatedly asked that you think belongs here, please let me know.
Q: Will I have to change my game to make it webclient-compatible?
A: Probably not. The only major things the webclient does not support are menu controls and multiple map controls, and some obvious stuff like client-side savefiles. Pretty much everything else should work, but check the documentation to be sure; a list of differences between the webclient and DS is at the end, and there's also a list of which skin parameters are supported. If you have a .dmf skin it should be translated automatically. Menus are a possible later refinement, although anyone could write a menu control of their own because the webclient is very extensible. (Currently menu info is not translated from the .dmf, but that may be added later so that anyone who creates a menu control would have it available.)
Q: Can the webclient run on a tablet?
A: Yes! Older tablets may have trouble, and there appear to be some issues with the default Android browser at this time, but mobile Chrome and Safari are capable of running the webclient. I've tested it myself on an iPad Air running iOS 7.
Q: But the webclient can do less than Dream Seeker, right?
A: While there are a few things the webclient does not currently support, that list is very small. The list of what it can do that DS can't is actually much bigger, and growing. The webclient is highly extensible in a way that DS never could have been. For the first time, you can create your own controls. They don't even have to be physical controls: You can define a class that does nothing but act as a game manager and pass info back and forth via winset/winget. You also get the power of a modern browser under the hood. While the server does the heavy lifting and manages multiplayer aspects of the game, clients can be prettied up with better-looking components than ever before.
Q: Do I have to write my webclient skin as a .dms file?
No. The .dmf skin, if present, will be converted for you by the server. However, if you do supply a .dms skin, it can be used to give the webclient a separate appearance than the one used for Dream Seeker players, and a .dms skin can also take advantage of any custom controls you might define.
Q: Can I run the webclient on my own site?
A: Yes. Dream Daemon will provide embed code for an iframe to include on your site.
Q: Will I be able to run my game on portals outside of BYOND, such as Kongregate, Newgrounds, Gamejolt, etc?
A: For any of those sites that support iframes, yes. The only caveat is that we don't currently interface with their login systems; webclient games use only BYOND accounts or guest accounts for the time being.