TL;DR: Smart move by Facebook that will make Vancouver more competitive in the long run.
Today Facebook announced a new technology office based in Vancouver. This will change quite a few things around here:
It will be more difficult for startups to hire new graduates from SFU, UBC, UVic and other tech schools.
Recruiters from Facebook and Google have been active at local university career fairs for a few years now. The FB offer just got a lot more appealing - while Facebook won't lower its hiring standards, many talented new grads can work for a Valley company without leaving Vancouver. This means median salaries are likely to go up a bit as well.
Facebook will bring a lot of talent from Canada and the world to Vancouver; many will stay here.
Some of the most talented engineers in Vancouver are from the prairie provinces, thousands of others (myself included) immigrated from all over the world. This trend is about to get an upgrade - it would be particularly great to see new grads from Calgary, Edmonton, Winnipeg and, of course, Waterloo move to Vancouver and stay here, instead of heading straight to the Valley. This is similar to the effect the local Microsoft office had on the city.
Another strong link between Vancouver and Silicon Valley will raise the bar for local startups.
The Facebook office will attract a lot of attention from senior talent, bring some of its engineers back home to BC (hey, Beau!) and generally upgrade Vancouver's visibility like the 2010 Olympics and TED have done in other areas. This will have a lot of nice secondary effects - more presence by Internet companies, more funding and more great advice for start-ups that are just beginning their journey.
Expect to see a lot of blue at Vancouver tech events a few months from now!