It looks like Google is handling the scalability issue very well with Google Analytics. They now allow you to to create up to 50 profiles. Typically you’ll have just one profile per site or subdomain but you can combine them if you want to. Google Analytics does not limit you on the number of websites that you can monitor but most users want to break-up the statistics so that they can view reports for each site individually, which is when you would use seperate profiles.
On a little bit of a sidenote I also noticed that their help section says that the maximum number of pageviews they allow is 5 million which is a lot more than the 2 million that they used to offer. If that is still not enough for you then you can create an Adwords campaign to track an unlimited number of pageviews. ;)