Sometimes updates are uneven because dependencies in Linux are shared and
there is no central registry. So a package may have an update, but a
dependency cannot be met and you get an error. This happens because
different package maintainers work on different schedules. One guy is done
his bit and the other is still working on hers. Sooner or later things even
out. So be patient. It can take days to fix some problems and others are
fixed more quickly.

The only time to worry is when you get a broken package. Then you have to
fix it or you cannot get any upgrades at all. There are two ways to fix
broken packages. You can do it from the commanline or from the GUI. Since I
don't know your package manager is broken then I will spare you the details.

I just ignore update errors till I update next time, they all seem to
work OK in the end.

If you mean 'update' , do I understand correctly you mean updating
repositories through 'sudo apt-get update' and updating packages for a
particular distro version using 'sudo apt-get upgrade' ?

I do the above twice a week and never had a problem (currently running
(K)(L)ubuntu 10.4