UPDATED: SEE BELOW
Over the past few days I have noticed that some of the component collections you find in your components window aren't accessible within Sketchup anymore.
It appears that all of the collections except for "Transportation" and "Playground" are effected. Since these categories are just essentially bookmarks to the 3D Warehouse, I assumed that Google had perhaps moved them online, and thus broken the link between Sketchup and where they reside online.
This doesn't appear to be the case, as these collections are easily accessible in your browser.
Since I use these just about everyday, I was really scrambling to find a way to get them back easily. After I found them in the browser I realized that I could download the models I needed, and then go to "File>Import" and select Sketchup models on the bottom, then select the component file I wanted. This is a tedious process at best.
The faster solution is to open a browser window next to Sketchup, find the components in the 3D Warehouse with your browser, then just drag them into Sketchup. This appears to only work on a PC, not on a Mac. Right now Mac users are stuck with the tedious method.
I wondered if anyone else was seeing this issue, so I checked around online and I found these threads:
Is anyone else seeing this issue? if so, please let us know in the comments. We will be keeping this post up to date as this develops.