If I had to name just one thing that impresses the heck out of me about SharePoint, I'd go with the power that SharePoint grants to the end users who manage sites. Sure, publishing, document versioning, the SharePoint object model and so many other features are pretty cool, but what you can do as a site admin or site collection admin is pretty dang impressive. You have the ability to control just about every aspect of your site, from who uses it to what goes into it. You are able to manage all of it from your web browser without any additional tools. And you don't have to be an experience IT professional to be able to do it.
In fact, this is so apparent in the current version of SharePoint that Microsoft changed their security model for sites to fully embrace this approach. In WSS v2 and SPS 2003 if you were a SharePoint Admin (someone who had administrative rights to the servers hosting SharePoint and all its administrative resources, such as User Profiles, Search, etc); you had the keys to the castle. You could access any site and make any changes to it you felt like, and no one could stop you. It was definitely an all or nothing proposition; your SharePoint admins could go to any site (such as an executive-only site) and view its contents. All in all, it was quite exhilarating 
Now in WSS v3 and MOSS 2007, as Lee Corso likes to say, "Not so fast my friend!" SharePoint administrators no longer have default access to your site. Each site collection can have a Primary and Secondary Site Collection Administrator, but that user can be anyone, regardless of their access. So in order for an administrator to get access to your site, he or she has to explicitly update those Site Collection Administrator settings to add themselves, which gets logged in SharePoint's security logs.
Now, as the title suggests, with Great Power comes Great Responsibility. Since you as a user have the ability to do a wide range of things with your site, you need to remember that you also have the ability to mess a lot of things up (not that you'd dream of doing something like that!). Something that's conditioned into IT professionals at an early age (we're all cloned in vats, in case you're wondering) is that you need to evaluate every decision you make and every feature available to your users in the platform you're administering. This is necessary because the choices we make can impact a large number of our customers in a wide variety of ways, and we need to make sure that the impact is as positive as possible. But now, to a certain degree, that safety net is removed and you are driving the bus.
This means that if you are a SharePoint site admin, you need to think about the choices you make in the configuration of your site. Sure, your SharePoint admins are going to make some decisions that will definitely impact your site, but the biggest day to day impact on how you and your users is now driven by you. This means that your mistakes can have a broader impact than just affecting how you use the site and the cleanup effort will not be as easy. I don't say this to scare you away from being a site admin, but because I feel like this is a warning that a lot of the site admins I talk to don't get.
ferringer