Here is a rather common question, "How big can my SharePoint 2007 installation be?".
Well, here is one thing to get used to with SharePoint - there are no hard limits (See SharePoint 2007 Limits). That doesn't mean there are no limits :), just no hard limits. But there are recommendations, which depend on what you are doing with the site(s).
So, how big can your Sharepoint site can be? Well that squarely depends on what you are doing with that content, and what kind of database cluster are you using to power the sites.
For instance, if you are doing a lot of versioning, editing/authoring, querying, then obviously the upper limit will be lower. But if you are using the site strictly for viewing, and no heavy duty querying - then the limit will be a lot higher. As a rough guideline, your content database can grow to 100-150 gigs without hiccups, and can go as high as 400-500 gigs with no hiccups if it is a read-only kind of site. And with enough pushing and customization, you can push this limit to 3-4 terabytes for a read-only site.
Okay, how big can your site collection be?
Now, an entire site collection lives in a database. So, as your site collection gets bigger - your navigation gets goofy, and you start hitting database limits (backup/restore, high availability, replication etc.).
So just as before, there is no hard upper limit, but if you are into thousands of sites in a single site collection - you need to seriously rethink your site structures. Again, this squarely depends on what are your sites comprised of, and what exactly are they doing. Don't expect sharepoint to be happy with 2000 sites with 1000 document libraries with 4 gigabyte video files in each. That will not work. Also, don't expect to not have to invest in a beefy SQL Server backend, if you are indeed running 2000 sites of even moderate content usage/size.
.. Finally, don't forget the magic "2000" number.
- Try not to return more than 2000 results in a single query/view on a list/doc lib. Use logical indexing to go beyond this number.
- Try not to have more than 2000 lists/doc libs in a single site (though frankly, 2000 lists/doc libs would create a nightmarish browsing experience, so wtf were you thinking when you put 2000 lists in a single site anyway).
- Try not to put more than 2000 sites in a single site collection.
- Try not to have more than 2000 items in a any folder in a list or a document library (which means, when using SharePoint as an ECM, don't put more than 2000 pages at the /Pages level).
.. once again, none of these limits are carved in stone. It really depends on "What are you doing with the content", not just the size of it.