Great thread.
Well, we have already discovered that life is incredibly opportunistic and lives in the most apparently hostile places here on earth. In fact it is looking increasingly as if life will exist wherever it possibly can, not just where the conditions are ideal.
That being the case there is almost certainly life on other planets.
Are there planets with advanced, multicellular, possibly sentient life forms?
Again, given the scale of the universe, this is likely to be the case. If there is life there will be evolution and if there is an evolutionary ladder, there are probably developed organisms. Some of them are possibly not that dissimilar to ourselves.
Deep-space planetary observation is just beginning and I can certainly remember a time when leading astronomers doubted if there even were other planets outside our solar system; it now looks as if we will discover more and more. So yes, possibly, somewhere in the universe, there are other beings out there who look up at the sky and wonder if they are alone.
Are we ever going to meet them? That is very unlikely. The sheer scale of space makes this impossible with any technology we know of. Even Gliese 581c, which is a mere 20 light years away--nothing in atromical terms-- is unthinkably far in terms of physical travel.
Think about this: we have been listening for organised radio waves for about 50 years. We have not heard any. Since any culture advanced enough to have developed deep space exploration technologies pretty much certainly has already developed radio, we can be sure that there is no such industrialised culture on a planet within 50 light years.
Now it is absolutely true that a planet say 1 million light years away (not very far in astronomical terms) might well have a super-advanced technology capable of deep-space exploration. But we would not know that because we are looking at that planet as it was 1 million years ago, probably long before it developed that technology. At the same time anyone there would be looking at an earth full of dinosaurs who do not emit radio waves so we're just another potentially life-supporting planet to them. It would be approximately 999,900 years before our first radio waves got to them and even if they sent a message immediately it would be ANOTHER 1,000,000 years before we got that.
That is a long wait.