CircuitLab is a new schematic design and simulation program that launched at the end of February 2012. A simplistic drag-and-drop component space is a slightly more modern take on the interface of circuit design software, compared to Multisim for example. The initial set of components is more than enough for those looking to get started with electrical design. Which might be the best bet, as building real world circuits for the beginner is often fraught with problems, errors, and quality issues that can be demoralizing. Their initial goal says it all: "We build the tools to help bring those systems from concept to practice faster, easier, and perhaps even make the process more fun."
For the more advanced user, CircuitLab cannot import Spice models of components for design and simulation. The CircuitLab support forum is littered with people needing to import component "X" into their design. Unfortunately, at the moment, there is little help for those users. However, the program is exactly 1 week old at the moment (3/5/2012), and Spice model importing is on MIT graduated founders minds.
I tested the web-based CircuitLab on several phones and tablet computers with no luck in getting the environment started. Standard desktops, in any browser, seems to be the only way to use CircuitLab.
A great effort for sure. I hope to see expanded functionality in the near future.