Re: How far away in space would we be 'visible' to ourselves?

Well, that depends how hard they are trying.  We have
the _technology_ to detect radio emissions at power levels 
similar to those we employ in broadcasting (a few megawatts 
equivalent isotropic radiated power, EIRP) but we do not
have the _money_ available yet to mount a search for such 
tranmissions at this high a sensitivity.  There are a few SETI 
systems currently in use, but with more modest sensitivity.  
Indeed, even as I write this note I am  observing a nearby 
star with the most sensitive of these systems, as part of 
Project Phoenix.  We can detect transmitters that have
EIRP's of a few gigawatts.  While that sounds awfully large, 
it is not all that much for highly directional transmitters.  
For example, I am using the 140 foot telescope of the National 
Radio Astronomy Observatory in Green Bank, West Virginia.  
If there were a similar antenna near the star I am looking at, 
it would only need a transmitter of a few tens of kilowatts 
to make a signal I could detect. Many of our more powerful 
radars and atmospheric research systems transmit with powers 
of more than a few GW.  So, while our current search is not 
as sensitive as we'd like, we still have some (unknowable)
chance of detecting other civilizations, either from broadcasts 
more powerful than we currently use (solar-system-wide broadcasting,
power satellites, terraforming...??) or because they are trying 
to get our attention with a directed signal. We are, needless 
to say, thinking about how to build systems of much greater 
sensitivity with a budget that we could have at least some
hope of obtaining.  Unfortunately, one of the biggest potential
sources of SETI funding, the federal government, no longer 
sponsors any SETI work, because a senator from Nevada doesn't like it.  
Fortunately, there are many private individuals who do, and who 
donate money and/or materials to support the efforts of the various 
SETI groups.  You can find more about Project Phoenix, as well
as links to other SETI efforts, such as SERENDIP and BETA,
on the web pages of the SETI Institute at: 

http://www.seti-inst.edu