I would definitely take the time to upload schematics to an image host when they're on a site which might change. If it's coming from Wikipedia or the like, then I won't bother. However, imgur is not permanent, either. From the imgur FAQ:
How long do you keep the images? As
long as images are getting at least 1
view every 3 months, they will stick
around forever. After that, your image
may be removed to create more space
for newer images.
Flikr and ImageShack both say that they'll keep your images for as long as you have an account, but that's not what we need. We need it to exist as long as the question exists, which means StackOverflow Internet Services hosting. Currently, imgur is used as a third-party image host. Does anyone know if SO has a special contract with imgur to keep images longer?
We need a simple schematic editor/local schematic host in the same way that MathOverflow needs an equation formatter. We've had a discussion on this before, but nothing really came out of it.
Edit: I just realized what it means for StackOverflow to have a code formatting tool in the editor. This is an acknowledgment that a site about coding needs a standard, hosted tool to share code snippets. Imagine if formatted HTML or various image hosts, (resplendent with the various background colors, highlighting formats, and fonts used by different programmers) were the only way to share code on SO. I think that it's hard to argue that our site is any different - We just need to work with schematics.