Lightroom is a pretty impressive piece of software.
Its semi-official purpose is to avoid launching Photoshop, and it works 98% of the time.
Even an amateur photographer today has maybe 10000 pictures in her collection, so it's reasonable that most Lightroom features are engineered to be scalable (up to some reasonable level).
For example, Ligthroom does not assume that the drive holding the files is always online; it seems not assume that the files are its exclusive property (it may be asked to watch for modifications to the .xmp files).
However using Lightroom in a "multicomputer environment" is still a major weak point.
In a "multicomputer environment", you need to be able to create a portable self-contained "snapshot" that contains all of your work, and pass this file around.
Consider this simple situation: I want to write a book, I have a Mac and a Windows-Pc and I need a reasonable solution that allows me to start some work on one, sync some files on my network, continue on the other machine. Let's say I use Microsoft Word: it's just perfect. File… Save as… Then I just keep the file (and some fonts) in sync.
Now I want to prepare a photography book with Lightroom. It's the same setup, isn't it? The same software on both machines… Wait, where's "Save as", here? :)
One of the non-advertised improvements in Lightroom 4 is that you can now open a catalog file produced by a Mac on a Windows Pc (LR3 used to complain about the different path format, and it didn't find the files).
So here's a first workaround: your files are on a network share of machine N (say, a NAS); machines M and W both point to N and you just sync the catalog between them.
But this may not be satisfactory: it requires three machines, and N should be the most powerful; also the machines need an identical setup: if you install additional camera profiles, you need to install twice.
In my configuration, for example, I have machines M and W, I do all the work on M, then for safety I copy everything (both pictures and xmp) on W. So I cannot just reopen the catalog: M and W have two different catalogs, each pointing to its own folder.
Even more, if I reopen a photo on W that uses a lens profile which is installed only on M, the profile is silently ignored.
(A similar effect does not happen with developer presets, but just because the .xmp contains only the final state of the image, not the history; however camera profiles and color profiles are part of the problem)
The fact that LR does not consider correctly "external references" as part of the self-contained work, is also evident in the lack of a dedicated search function.
I'd like to be able to find all the photos that use lens profile X, camera profile Y or developer preset Z.
So to sum up: some reasonable improvements that I'd like to see.
1) an easy way to transfer contents between two instances of LR
2) create a really portable and self-contained snapshot
3) find references to "external files"
4) an exif editor and an exif configurator (say I want to import/export additional tags)