1) You need to make the final output embeddable, like slideshare, so that people who are creating schematics using your software are able to put it on their blogs and website
2) The embedded version can have a link back to your site, e.g. "Modify this circuit" or better "Run this circuit" so that you get backlinks and the visitors can interact and come to your site.
3) You are 100% correct with the "try it now" button, but instead of redirecting them to a signup page, try using a modal popup over the circuit. I'm sure you'll see a good increase in signups with a split test.
4) You can also create a shareable URL (like tinyurl) where even without signing up a person can send that URL to a friend or post it on twitter/facebook. This will get you even more traffic / backlinks.
Just a few things on the top of my mind.
[Edit] A grid would be killer too; great suggestion.
[Final Edit] Tooltips on the components/actions would help your goal of making electronic design simpler/easier to do.
Selecting: Hold down shift and left click elements.
Box select: Hold down shift and drag a box around the elements to be selected.
Deselect All: Left click on the canvas.
Move Element: Just drag it.
Connect Terminals: Drag from schematic terminal to other schematic terminal.
Disconnect Terminal: Left click terminal. Click 'X' .
Rotate Element: Select element and push 'r'.
Remove Element: Select element and push 'del'.
Flip Element Horizontally: Select element and push 'h'
Flip Element Vertically: Select element and push 'v'Definitely contact us if you have any trouble.