I hope that I have not hijacked gunnar1's thread and that this is contributing to their original post.
I'm sure he won't mind.
This is how I see it (with the caveat that I haven't tried any of this as I have only
one catalogue shared between two computers).
There are two sorts of metadata:
1) The sort you write (keywords,IPTC info etc)
2) The sort the camera writes (Exif data etc)
The sort the camera writes is included in the raw file and you can't usually change that. The sort you write goes into the LR catalogue. There it can't be accessed by other programs (Bridge etc.), so if you want the metadata to be accessed by other programs or to travel with the images when they are exported to another catalogue, then the metadata needs to be written into an xmp sidecar file for each image.
To do this you can go to: File - Catalog Settings - Metadata and tick the "auto write" box. So now you don't have to worry about updating sidecar files. The big disadvantage of doing this is that you have to wait while the metadata is written, and it can really slow down LR. So many people turn this option off.
So before exporting images you may need to save the metadata into the xmp sidecar file. Select the images you are going to export and go to: Metadata - "Save to File" or hit Cntrl S.
You can see if there is unsaved metadata by going to: View - Options and ticking the "unsaved metadata" box. Now if you see an arrow in the top right of an image that's pointing downwards, click on it to update the metadata for that image or for all the selected images.
Say you now go to : File - Export as Catalog, and you put the images into a file on your desktop. If you look in that file you should see your Previews, photos with xmp sidecars, and Catalog file. You may need to go to Folder Options and select "show hidden files" to see the xmp files. I don't know. If you then open one of the images in Photoshop, ACR should see your metadata and image adjustments. If you delete the sidecar file and reopen the image, just the original raw file should be left.
After you import the catalogue into the other computer, you should see upward facing arrows in the top right corner of images that have had metadata added. You need to get this into LR from the sidecar files. Select all the images and click on an arrow (you may get a "metadata changed externally" message - yes, it was`done on the other machine). Choose "import settings from disk" and you are done.
If you convert your images to DNG, you don't have this bother. But I can't get a workflow going that that does what I want with my images, so I have scrapped DNG for the time being and am sticking with the CR2 files. I also never update my sidecar files as I only use LR and Photoshop. I found Bridge slow and buggy and I just don't get it.
Hope this helps and I haven't made any major stuff ups.