I looked at the circuit too, and I'll add some move caveats:

C3 absolutely MUST be specifically rated as an Across-the-Line capacitor.
 C3 is where the line voltage gets dropped down to the Vcc level.  If
this cap fails shorted, something will blow up (quite literally).  Line
rated caps will not fail shorted.  Don't make the mistake of assuming
that R1 is to protect you from this.  It will dissipate about 300 watts
if the cap shorts, which will probably cause it to explode.  R1 is there
to limit the surge current when you plug this thing in.

If you want to connect this circuit to any other devices, be very careful
of grounds.  JP3 pin 2 is connected to the line voltage neutral.  This
can be several volts or more different from ground.  That's enough to
damage your equipment or make it act wierd.  Opto isolators would be a
very good idea.

This circuit switches the neutral line, which is normally not the correct
thing to do.  It means that when your lamp is off or partially dimmed,
both sides of it are HOT, which I think is a violation of NEC rules and
is an electrocution hazard.

Your switches should be carefully selected to ensure that the contacts
cannot be touched, even if the switch breaks, as many inexpensive
switches will do when there are kids, pets, or clumsy adults around.  If
your circuit is built and functioning correctly, there's little danger,
but if you plug it in backwards or if something fails, those contacts
become HOT.

I agree with David Fansler's wiring recommendations, except for one - if
you are in the US, or probably anywhere else, NEVER connect ground to
neutral.  Ground is a separate circuit designed for your safety, and
should never be used to carry current.  If you connect it to neutral,
will reduce its effectiveness.  Also, you may reduce or defeat the
effectiveness of GFCI breakers, which are now required for certain
outlets in most US home construction.

Speaking of GFCI breakers, I would recommend that this circuit be plugged
in through one.  It will reduce some of the dangers mentioned above.