[QUOTE=BROO]1. I need a possibility to import/export save game data into separate file(s) (using external app). Is there a way to figure out webstorage's local data location for my external app?[/quote]
I don't think WebStorage has any particular location on disk, but HTML5 is getting a File System API which should help. Hopefully a plugin will appear for that in future.
[quote]2. What are the disc space limits for webstorage data stored on local machine? Are they browser-specific? [/quote]
It's browser specific, and I think it was around 5 mb... WebStorage was intended as a replacement for cookies.
[quote]3. Can the data stored locally be considered safe?[/quote]
I'm not sure when it gets cleared - you might want to test if clearing the cache frees it, because the AppCache (offline support) isn't cleared by clearing your browser cache I don't think. Also, as far as security goes, all webstorages on the same domain share the same storage. So all HTML5 apps on Scirra.com use the same storage.
[quote]4. I'm making an offline game with Construct 2 (not utilizing any of the HTML5 features).[/QUOTE]
What do you mean by making a game in Construct 2 not using any HTML5? Games in Construct 2 use HTML5 specific features (like canvas) to run at all, you can't run a Construct 2 game without HTML5.