Well I'm going to be a totally unoriginal shill and go along with:
IT FUCKING DEPENDS.
I'm not worried about 'Space AIDS' or the like because diseases have to co-evolve with the host species to be infectious. Considering that a true alien will have evolved completely separately from us the idea of something being able to jump biochemical lines that severe strikes me as...unlikely to the extreme. Throw in issues like 'right-handed VS left-handed amino acids' and 'genetic codes based on a chemical other than DNA' and it rapidly approaches outright impossibility.
Having said that I'd probably be willing to do it if:
1) We're compatible mentally. Meaning for example that while a hive-minded race might be possible in theory where each individual unit is not sapient in of itself but the sum of its parts IS I somehow doubt that it's mental processes will even remotely resemble anything we'd recognize and it might even be impossible for us to understand each other on a deep level at all.
2) We find each other physically appealing to some extent and our respective anatomies allow for mutual stimulation and gratification. This I shouldn't have to explain too deeply for obvious reasons.
...but I will anyway...
Sufficed to say that if somewhere out in the universe convergent evolution has brought forth a sapient race that follows a bipedal (Or possibly hexapod, I'm not that picky.) body layout, nurses their young through mammary-like glands that are persistent regardless of fertility, exchanges genetic material through "Insert tab-A into slot-B" type genitals involving a "Pleasurable for both parties 'Horizontal Boogie' " type process, and due to their original ecological niche and no small amount of luck strongly resemble certain Terran apex land-predators then I'd be more than willing to totally tap that space catgirl booty.
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Also, relevant and obligatory Penny Arcade reference:
http://www.penny-arcade.com/comic/2007/9/19/
.. like skydiving is an experience .. but this is a doing it with an alien kind of experience
