6! This has got to be one of the biggest sites and definitely the biggest English speaking forum (I can't speak about other languages). How can we increase this? No wonder I didn't hear about this forum for months when I was a bitcoin newbie!
I am not sure if you realize that google searches are personalized. It depends on location, previous searches, browsing history etc.
There are many factors which determines site positioning. For example: if I seek word "bitcoin" - bitcointalk appears on top of 4th page.
I was curious and tried this with DuckDuckGo, a private search engine that doesn't track you. Bitcointalk was at the bottom of the first page. It's probably because of either bad search engine optimization (SEO), or the fact that sites with just "bitcoin" have more weight, as it is more directly related (bitcoin.org/bitcoin.com were at/close to the top). If you search "bitcoin forum", bitcointalk appears at #1, above bitcoinforum.com, probably because it is a lot more popular.