There's an interesting debate with Frank Drake and various experts on the likely emergence of intelligence at http://radio.seti.org/past-shows.php
Go to to the sound file at March 17, 2008 "Formula One: The Drake Equation".
While I believe simple life may be abundant throughout the universe, I expect that 'intelligent' life is very rare. By 'intelligent' I mean having the ability to build radio receivers/transmitters. It took life on Earth 3.5 billion years to manage this with only a single species emerging as capable. Although apes and dolphins have 'potential', I think they are already too closely related to us to seriously be seen as separate data points. Remember that it took around 3 billion years of life on Earth before highly complex organisms evolved. Still, there only has to be one civilization per galaxy to make 100 billion across the universe.
The only other animals with 'potential' are the cephalopds, particularly octopuses. Their intelligence is obvious, although difficult to measure perhaps because their type of intelligence is so 'different' to our own. They are a very rare example of intelligence evolving separately from ours, which gives me hope that life outside the Earth isn't all just slime sloshing around in some murky alien ocean.
