For me, my idea about rolling update was easy to understand, system is always updated day after day, month after month, each software is updated when it's needed...
The fact there are UP makes me surprised. UP is in my head like a Service Pack 1-2-3 for Windows XP for example. Then some bigs updates/upgrade on 1 time, that can make a lot of mess in the system during 1 update/upgrade with 1 UP.
I'm ok stability is nice, security too.
For me, I think it's easiest to update when there's an update available about a software: you can know it's apache2-common you updated is causing troubles... In a big UP, you don't really know what can be the problem.
I'm not dev, just a end-user :p
I saw Sobrus writing:
I don't really want to install 300MB of useless stuff daily on my write-limited SSD
I think 2 little updates by week = 1 big UP sometimes to decompress/uninstall old version/install new/clean temp
Ok, the 3 updates for apache2 will result in 1 on an UP... But I'm not sure today's good SSD a so little lifetime