If Dr Drake shares your view that we are alone, he must have come to this conclusion quite recently. Here is part of an interview he held with Der Speigel on 12 June 2009:
" ONLINE: Mr. Drake, after searching for decades, no extraterrestrial signal has yet been found. Are we alone in the universe?
Drake: We are definitely not alone. At the same time, I think it will be very hard to find the extraterrestrials. If they are only slightly more advanced than we are, they may be using technologies that don't reveal them. Not because they are trying to hide themselves, but because of the fact that every evidence that we find of extraterrestrials has to come from some form of energy that is wasted. If they are clever, they will be using technologies that do not waste energy."
http://www.spiegel.de/international/world/0,1518,629411,00.html
DG, I think you are deliberately misreading my posts. I have not said Frank Drake has changed his mind about a SETI signal. I said Frank Drake recently stated in an article that if a SETI signal had not been received within the next 25 years then (at that point) Drake suggested we would need to consider in the absence of such a signal, that we are alone. Unfortunately I cannot find the said article. However, the essence of what Drake is saying is this, in 25 years time, SETI would have been searching for nearly 70 years. Each year has seen increasing more sensitive equipment being used and millions of radio frequencies listened to, by such equipment.
The Allen Array would probably be bigger than it is now, We'd have refined our earth size planet hunting by Kepler and potentially other missions. SETI is as you point out, also looking for artificial light signals from an intelligent civilisation.
By the end of the kepler mission, we should have a very good idea how common 'our' type of solar system is. I contend the evidence we have so far, based on 400 exoplanets found todate, that the informations points to our solar system is not the norm. Nearly every exo system found to date has hot jupiters. While this doesnt preclude the formation of earth type planets in the habitable zone, it does in all the simulations run result in earth size planets being ejected from that solar system.
If all these searches are pointing to the same conclusion their is no other technologically advanced civilisation then, we are probably alone. At the beginning of this thread, my post mentioned Fermie's Paradox, the Rare Earth Hypothesis, Von Nuemann Probes and Bracewell Probes. I have also mentioned dyson spheres.
You simply cannot say a reasoning that we are alone or, possibly the most technologically advanced civilisation in the galaxy right now is based on a single premise. What Im saying is the evidence is mounting. Fermie's Paradox, if the galaxy is teeming with life, where is it? No radio or light signals detected. No evidence of VN or Bracewell probes, no evidence of dyson spheres, no solar system yet found that is not of the hot jupiter model, the Rare Earth Hypothesis which, argues even if there are millions of Sun like stars in the galaxy, the likelihood of another earth forming around it and developing an intelligent civilisation within the same time frame as us is questionable.
My premise is, although there may have been past intelligent civilisations in the galaxy and may well be after we are gone, the probability is that we are the only intelligent civilisation in the galaxy right now.