If you're Google, waiting until you absolutely know you need a specific talent seems like an approach that would definately keep fresh innovative ideas and creativity out of your company.
Imagine a young Mark Zuckerberg going to Google for a job. Zuck says "I got this great idea for social networking for college students." Google HR says "We don't have a position open for that right now. Plus you don't have a good resume and you're not a fancy-pants PhD. Don't call us. We'll get back to you." Zuck goes down the street, continues to work on Facebook, and then promptly hires away all of Google's employees. The rest is history.
What I want to hear from Google right now is "Patrick, we don't have a specific job for you yet, but we would rather hire you now anyway to prevent you from accepting an offer elsewhere." But that'd just be too damn easy, I guess.
It's easy for any of us to say we're a talent - it's how you show that you're a talent that will make you attractive to an employer (not only just Google).
At least you know they're looking at your application - I graduated with a political science degree in December and have been sending steady streams of applications for months with nary a peep from Google recruiting.
"The Google Resume" is a great book. It's written by a former hiring manager that's worked at Google, Apple, and Microsoft. Gayle Laakman also wrote "Cracking the Coding Interview" and runs www.careercup.com .
Nobody gets hired by sending "steady streams of applications for months". You gotta stand out somehow. In my case, I run two websites that track over 300 start-ups. I was also personally referred to Google by a Stanford PhD already employeed by Google Research. Google has no excuse for not inviting me in the 'Plex.