I've immersed myself in Microsoft's Windows SharePoint Services and SharePoint Portal Server. This is a great product. For my current client, we are building an Intranet Portal system for their employees to have access to all sorts of information. The solution includes document management, security, targeted content, and much more. And, we're building it in 3 weeks.
My company used to butter its bread building intranet solutions from scratch using ASP and SQL Server back ends. A solution like this could easily take 6 months or a year to build. And it wouldn't have the level of functionality or customization that a SharePoint implementation provides.
I think it's a great product. However, it is not without its faults. Some things that seem like they should be so easy to do are not. For example, if a company has an external timecard application, it should be able to notify users in SharePoint that they need to approve a timecard. So far, I have not found an easy way for this to happen. I have tried to set up a custom list for all of these notifications, and then each user must then subscribe to receive alerts from this list. That works, but it isn't quite as functional as we would like.
I was hoping the Alerts OM would expose a method to allow external apps to create new alerts targeted to specific users. I haven't found that yet.