SharePoint content databases can be any size. There are no hard limits.  There - I've said it.

I hear customers and partners still claiming that there's a 50GB size limit. There is NOT. It's a guideline, not a rule. Let's say you want to store 1TB of data in SharePoint...no problem. You could have 2-3 content databases with 400GB each. Or one very large content database. SQL 2005 and MOSS 2007 would handle that fine.

So why the limit?  Managability. It's simply faster to restore smaller databases.

The 50GB myth comes from a practical limitation that administrators put on themselves; it's simpler and easier to manage a SharePoint environment when databases are small. Many customers I work with still don't have the hardware, people, and time that they need to have a real recovery plan.  Why?  Because in many cases, SharePoint grew out of pure business need and caught on like wildfire. I know large customers who are still running SharePoint like a departmental application. Once they realize that it's a business critical application - at enterprise scale - governance (along with funding) is added to the master plan.  Do you want to convince your manager or business lead (i.e. the one with the budget) that you need more resources?  Shameless plug: get them a copy of my book.  They will understand SharePoint better and realize the need for governance, planning, and better resources for IT.

One more thing: If you're looking for a better way to backup and restore SharePoint, especially for large databases, check out Data Protection Manager 2007. Why? It supports change-only, agent-based backups and single site/single file restore in WSS 3.0 & MOSS 2007.  I'll be doing some testing with large content databases over the next couple of weeks and sharing my results.

In the meantime, here are some great posts by Joel Oleson on database and site collection sizes:

Content Database Size:  http://blogs.msdn.com/joelo/archive/2006/08/01/684691.aspx, http://blogs.msdn.com/sharepoint/archive/2006/08/03/687995.aspx

Site Collection Sizing: http://blogs.msdn.com/joelo/archive/2007/01/31/tips-on-site-collection-sizing.aspx