The documentation at http://dev.w3.org/html5/spec/offline.html#disk-space states that "care should be taken to ensure that the restrictions cannot be easily worked around using subdomains", so one would really have to use different domains as you write, which sounds a bit costly.
I think Opera Mobile shouldn't have this cache problem either, similar to my comment about the desktop version. The default cache limit in Opera Mobile is ~2 MB.
I _believe_ that both quotas can be increased after confirmation from the user, but I haven't made any tests.
I don't think either notifies you about the background transfers, but e.g. Operas default cache limit for Application Cache is ~50 MB according to http://www.opera.com/support/usingopera/operaini/.
This is not an issue in either Opera or Firefox. The title should probably reflect that it's limited to Chrome (and possibly other Webkit browsers + IE?).
Edit: The numbers are only for the C implementation so they don't add much to the discussion. Sorry for posting too quickly!
I don't know about this library in particular, but there's some numbers available on http://liblzg.bitsnbites.eu/ for a similar library.
(The same author has also made a library for self extracting javascript code: http://crunchme.bitsnbites.eu/. Pretty cool, but probably not that useful outside of the demo scene.)
You can escape the purely functional part (to do IO for example). This library does however provide 2 implementations: one in the IO monad and one in the ST monad.
If you use the IO monad one then you can do whatever side effects you want. It's up to you to use the rest of the code in a responsible way (which means that you can write code C style if you want).
The ST monad version is quite nice, it lets you use the hash table as if it was modifiable, but only inside the ST monad. Looking at it from the outside, it's still purely functional, and within the ST monad you're restricted to purely functional programming and the facilities provided by the ST monad. This makes it a safe alternative when you want to use a hash table for performance reasons but still want to limit what side effects that can be used.
The documentation at http://dev.w3.org/html5/spec/offline.html#disk-space states that "care should be taken to ensure that the restrictions cannot be easily worked around using subdomains", so one would really have to use different domains as you write, which sounds a bit costly.