I ran into the issue many others have mentioned in this thread while going through this exercise, first mentioned in skought's post.  As the video was created during the (early?) beta process some of the instructions no longer apply to the GA product. 

Specifically I followed the instructions to have the DLL file (aka assembly) written out to c:\inetpub\wwwroot\bin.  This folder is there in my machine and the build put the file there without any trouble.  The correct location of the file on my machine is:

c:\inetpub\wwwroot\wss\VirtualDirectories\80\bin

Also, when it was time to edit the web.config file it was not in the folder specified in the video (c:\inetpub\wwwroot).  Instead the proper folder to find the file to edit is:

C:\Inetpub\wwwroot\wss\VirtualDirectories\80

Like some others I did a search for all instances of web.config in the c:\inetpub\wwwroot path and modified multiple instances of the file.  It wasn't until I put the actual DLL file in the correct bin folder that the web part actually showed up for me.

c:\inetpub\wwwroot\wss\VirtualDirectories\80\bin

While I was frustrated by the fact that my web part wasn't working when trying to follow along with an extremely elementary exercise, I have to (grudgingly) admit that I learned more about the whole process by having to repeat the steps multiple time and beat my head against the wall in frustration.