About a month ago, Microsoft Live passed MSN in daily rank; you should expect to see this reflected in Alexa's three-month rank any day now. The next sites in line for succession --- MySpace and Facebook --- currently lack the reach to upset the Top5. In the middle of this Microsoft dance are Google and YouTube. The following graph illustrates some interesting trends.
As you can see, for the last five weekends YouTube (in teal) has out-ranked not only Live (in black) but also Google (in red), making it the #2 site on the internet. This raises two questions: 1.) Really? and, 2.) Why? To understand this trend, let's first take a look the corresponding reach and traffic graphs.
These graphs show that Google always has more unique users per day than YouTube but that every weekend, Google loses traffic whereas YouTube gains. This is not so far-fetched: the other search engines in the Top5 --- Yahoo! and Live --- show the same general trend. In fact, youtube.com has (for several months) had more overall traffic than google.com. This is also not far-fetched because of the different natures of these sites. When people go to Google, they are searching for content that is likely elsewhere. On the other hand, people that go to YouTube are going for the content on YouTube. Taking into account that (in general) search engines are a means and video sites are an end, it is not unreasonable that YouTube could get more pageviews per user (and more traffic) than Google.
This isn't the whole story, though. Another big difference between Google and YouTube is the way they use international domains, or ccTLDs. If I go to http://www.google.co.uk, I get the British version of Google and that traffic counts for google.co.uk, not for google.com. If I go to http://www.youtube.co.uk, I get redirected to http://uk.youtube.com and that traffic counts for youtube.com. In the Alexa Top100, Google is represented by their .com plus 19 ccTLDs. Each of these international sites pulls in between 0.1% and 0.3% of the daily traffic Alexa sees. Adding that to the 2.2% pulled in by google.com, Google's search sites get at least 6.0% of daily pageviews, which beats YouTube's 3.0% hands down. (Also of note: this beats Yahoo!'s 4.8% and they pull the same ccTLD trick that YouTube does, when possible. There are some exceptions --- yahoo.co.jp is an example --- due to individual registry rules.)
So the answers to the questions posed above depend on what you mean by "Google," i.e. whether it is a site, a brand, or a company. The first would be only google.com; the second would include google.com, google.fr, google.com.br, google.de, etc. The last would include those properties plus YouTube, Orkut, Blogger, et al. The point is that those are important questions to ask when doing traffic analysis on the web. Be wary of analyses that fail to take these kinds of issues into account, especially if the analyst incorrectly uses statistics. (Luckily, some people get it right.)