<p>I'm trying to wrap my head around SharePoint.  Why is it good?  Why is it bad?</p>

<p>At a glance it appears to offer some incredible collaboration tools.  However, the cost looks astronomical and it seems to be rigid &amp; difficult to customize.</p>

<p>To those who've worked with SharePoint; please describe something good and something bad about it.</p>

It has pretty good Office 2007 integration. As an example, Excel understands when you have a file checked out and will let you check it in (with comments) when you close it. The document management features simplistic version control (although it's not required; you can go with a single version for each file).
In SharePoint, everything is essentially a list internally and it's very easy to create a custom one. On a related note, I haven't used either yet, but it supposedly works well with workflows and InfoPath.
On the downside, it's pretty much a resource beast. It requires multiple machines with powerful specs, particularly if you want to "really" use it for document management and to be the backbone of your intranet/internet site. It scales to an extent, but it's not pretty from my vantage point.
Customizing it presents it's own challenges. You really need people focused on it full time, as both administration and customization require their own impressive learning curves.
Lastly, some of the out of the box parts are poorly implemented. The wiki is a prime example; it's basically useless in my opinion. So one thing to keep in mind is that some may consider SharePoint as a whole package as "best in class" (not saying I do!), its individual features often are not.