Since the original Legend of Zelda (circa 1986… jeeze, has it been that long?), save systems in games have become ubiquitous to the point of being a requirement. So obviously, 4kg will have a well-rounded saving system. I want to point this out because there are several HTML5 games I have tried which do not take saving into account, which is almost completely unacceptable unless you’re making a kind of arcade-type game. And even then, high scores and unlockables, you know?
Even those that have save systems I feel do not get it truly right. In an age where computers are almost a commodity and people switch between multiple PCs every day, merely storing save data locally is definitely not ideal, especially taking into account how cloud-centric the rest of the web has become.
So that’s why 4kg will be incorporating cloud game saves. Although you will have to manually set it up (like Chrome’s syncing), once configured, your save file will be persistent across any number of Chrome instances.

It works like this: you go to the options page of 4kg (similar to other Chrome apps and extensions), and choose to sync your game saves using your Google Account. (Other accounts are not a possibility, initially at least.) Specifically, it is saved as JSON to your Google Docs account. Then when you play 4kg on another computer, you do the same thing, and whammo. Over the air magic. Even your fullscreen settings are persistent!
As for the system itself, you will have three slots for save files per game (or sync’d account.) Data is saved at the completion of a level, and you will be able to delete a file at any time of your choosing.
I believe this system represents using the web to enhance a game to its maximum potential, and look forward to hearing your feedback.
-Andrex