I don't know what you call the bit of the installer that copies .deb
files onto disk. please reassign as appropriate.
I chose manual partitioning because I wanted to preserve a WinXP partition
(something _has_ to be done about that first option screen in partman, ugh). I
set /var to 512Mb, easily big enough for a normal debian install. But not big
enough for ubuntu, it turned out.
When the package copying failed, I was lost. The installer didn't offer me an
obvious next step. All I knew was that it had said something had gone wrong, and
thus the installation was likely doomed. After caffeine I did the obvious and
redid the partitioning with /var twice as large. Noobs aren't going to cope with
that,
they will need some guidance.
It would help usability a lot if the installer calculated the disk space needed
by the package pool it wants to copy and ensured that
/target/var is big enough. If you stop, explain the problem and suggest going
back to partman (even suggest a min. size for /var),
I think most people will cope and be gobsmacked by the brilliance of the installer.
The general problem with this kind of thing is that Debian packages don't come
with a fine-grained enough breakdown of the sizes of files installed into
particular partitions to answer the question "do we have enough space in /var?",
at least not without some very processor- and I/O-intensive computation.
However, it would probably be possible to work this out in the specific case of
the "Copying remaining packages to hard disk" step, and that seems like it would
be a good idea. Reassigning to archive-copier.