People believe a lot of strange things in this world. They worry specifically that SharePoint won't perform as well as they need, and that they can write some sort of ASP.NET app with a SQL backend that will somehow outperform it. I really liked this post from Eric Shupps that lists a few of them. Keep in mind these are all myths - that is "not true".
- SharePoint Lists Have an Upper Limit of Two Thousand Items
- SharePoint Is Just Too Slow for Common Tasks
- SharePoint Is Not Suitable For Large Public-Facing Web Sites
- SharePoint Isn’t A Scalable Enterprise Document Management System
- SharePoint Pages Take Too Long to Render Over the WAN
Eric goes into quite a bit of detail debunking each of these 5 myths, so if you have a tendency to believe these things, here's a chance to get straightened out on that.