It is a good educational resource. I know I just taught a one day course in basic circuits and I would have used this instead of SolveElec.

(Note: I'm one of the developers of CircuitLab.) I believe a parallel question would be: are the "serious work" users avoiding cloud-based software such as Google Docs, Dropbox, Github, Basecamp, and even Gmail?

Where my money depends on it - yes, actually I do avoid them. (apart from github - since they're easy to replace when needed/down) If I can't have a local copy, it's too dangerous.

Still - great for testing stuff out quickly.

Honestly, somewhat. Dropbox and Gmail are seen as fine with less sharing with the internet and more about just having your personal service online, whereas things like Google Docs and Github less so. Even then, you try to avoid using Gmail to send sensitive material(Not to mention actually sensitive in a legal sense).

I think you and viraptor are right -- the answer is still "yes/somewhat" to avoiding hosted solutions for a lot of people, and especially companies. Ten years ago, many small-medium businesses had their own IT staff running an email server, file storage, and maybe even a little intranet site. Many still do, but I'd guess the fraction has gone down significantly as companies slowly get comfortable moving some of their bits out of the building. (Key word is slowly.)

But it's happening: I'm sure there are tens of thousands of HN readers who today keep their important data in hosted source code repositories, hosted accounting/invoicing packages, hosted CRM services, hosted e-mail services ... where both the software and the data do not necessarily live on their own machine. It hasn't happened as much in creative or engineering tools yet, but in my opinion, that's rapidly about to change as browsers become more and more capable platforms for powerful apps.

Furthermore, the line between "my software" and "cloud software" is being quickly blurred from both sides. From the existing desktop players, consider Adobe's Creative Suite becoming a subscription service / SaaS (http://news.ycombinator.com/item?id=3877191). And from the web apps side, consider that if we knew that people were willing to pay enough for it to be worth our time, we could package up CircuitLab to run as an offline app (already in the Chrome Web Store, but requires connection right now https://chrome.google.com/webstore/detail/haghanbgfkfpmepooh...).

At Tinkercad, a cloud based solid CAD system, we see "serious work" happening in a cloud environment.

Absolutely, every place I have ever worked for avoids this kind of things.