Extraterrestrial Life - Earthlike or Not?

I happened to be watching a TV Prog on C4 yesterday about the possibility of ET. A leading astrobiologist (sorry, can't remember who they are) stated a theory of his:

Look at life on Earth. Out of all life on earth there are only 3 different types of eye. That is in all creatures on our planet. Humans and squid, despite evolving completely independantly of each other from basic single and several celled organisms.
apparently this shows that when presented with similar conditions to those on Earth, if the ingrediants of life as we know it (carbon, amino acids etc.) are present, it is inevitable that evolution will take a similar route to that on earth, and the life on that planet will be 'eerily similar' to that on our planet.

I'm not a believer, but this could be a possible explanation for Nordics, Greys and other humanoid aliens.

The other theory, the one i held completely until hearing this other one yesterday, is that alien life would be competely unlike that on earth, some much so we may not even recognise it as life.

The way I see it, it is possible for both these hypotheses to be true, in fact they rather compliment each other. The evolution of life on Earth-like planets may be like that on Earth, yet life as we do not know it may exist in completely alien (in its true sense) forms.

What do other people feel about this.
I'm generally fairly skeptical on alien topics, not being a greys/blues/nordics/reptilians etc. believer, but i can see the sense in both of these topics from a scientific biology/astronomy position.

actually, a group of scientists created an equation that would single out how many planet in a galaxy would have life and just what kind of life would evolve. you'll have to do a google, because i'm troo lazy to put a link.

also, it has been assumed that there could be silicon-based lifeforms, as we are carbon-based, and both silicon and carbon appear in the same column of the periodic table of elements. so one could say that a silicon-based lifeform would in fact not really look like a life as we know it, most likely resembling some sort of rock or metal. assuming, that is.

Primitive life can come in lots of forms just look at the criters science gets from the DEEP ocean. On the other had intellgence life that Creats is a whole different ball game. (intellegent life that doesent creat can take on any form as well but we would NOt be able to relate to it .) Dolphens just how intellegen are they?
anyway for intellegence to be able to creat the simplest tool requires a way to maniplate the tool . In other words a hand of some type with fingers of some type . No hands no way to creat check out your dog.
also the hands need to be free most of the time .In other words the more you can use them the better you get at using them . Thus you must walk up right . So now we have a criter that walks up right and has hands of some type . Ok how far can we go with this ? just two hands or more? just two legs or more?
well more then two each then the brain power is used in contrioling the hands and feet leaving little left over for creating. so this takes us dow to six max more then likly and for total would be more balanced .two hands two legs. Check out ALL higher form of life of earth.
so now we have a criter that has two legs two feet and stands up right all we need is brain power . Lets give him a walnut opps Moron stands there staring . Ok so lets give the poor criter enough brain power in order to be able to creat now we have a brain near our size or larger .
Criter is looking more like us by the minit now. how about 4 eyes? two mouths? three noses ? not very relistic is it nature is not very redundent and only gives enough to make it work. so were back at two eyes one mouth one nose. There is NO higher lifeform on earth without this set up to one degree or another . So unless the bugs find a way to get lungs and internil skellitions then the logical conclusion most intellegent lifeforms will follow this patteren.
But lest we forget this is a BIGGGG universe and anything -everthing is possible . so in general most will look much like us there are probly manny we wouldent even relize are alive.

This website talks about a scientist who is publishing a book about the possibility of silicon-based life froms living under Earth's surface, and possibly also outside our planet. He believes efforts should be made to discover if these underground silicon-based life forms exist, possibly to help theories of extra-terrestrial silicon based life forms seem more feasible. Now, we haven't discovered many, if any, planets like our own. If there are planets that support life like the way ours does, then I think the native extra-terrestrials would look similar to us, assuming the theory of evolution is correct. However, if all other planets are like the majority of planets we've discovered, with hardly any, if any oxygen at all, a lack of sunlight or too much, an abundanc of chemicals and things that we cannot survive in, then I think it's more probable that any life surviving on thos eplanets would be...I dunno, like tape worms, or even just bacteria and stuff. It's still extra-terrestrial life, even though it's kind of boring.