The biggest advantage that comes with being a Y Combinator startup is that it brings many aspiring founders together which leads to a healthy exchange of ideas and information. It helps the startups find their way across any interruptions and steers them in the right direction.
One thing that YC wants its participating founders to do is to move to their location for 3 months. This becomes a limiting factor when it comes to people wanting to start startups in countries other than US.
It seems YC is already thinking about expansion plans outside US:
Actually, the seed funding business may even be international. We'll see. But for now at least we're waiting to decide what to do about other countries. (source: http://ycombinator.com/faq.html)
It will be interesting to see YC expand into international space and help more and more startups flourish. IMHO, YC should start conducting Startup School at international locations, at least on an experiment basis. Who knows where they find next Google?
Current music: Scientist by Coldplay