Hi 
Some of you may know of KTechlab while it will be new to others.
Among other things, it is an intuitive and easy to use circuit simulator that runs in Linux.
The development has pretty much be dead for a few years, but the main developer Zoltan has put in a huge effort to update the code to QT4 and modern Linux distributions.
If you're a Linux-user like me, you've probably been searching for a nice, simple circuit simulator but to no avail.
Give it a try and perhaps join the mailing list to help with feedback
Regards
Claws