stayed on 9 (currently 9.5.4) on primary servers which host important projects
Do you know if 8.6.0 will (smoothly) upgrade to 9.5.4... if the day comes for me??? (I only have about 150 client domains)
We upgrade 8.6 to 9.5.4 quite frequently on Virtuozzo (but not using any of the Virtuozzo tricks for doing this). Its gone wrong once out of probably 50+ because my instructions weren't followed to the letter (don't copy/paste the commands all at once).
That said we've probably not upgraded a VPS with 150 domains, 100 domains will have been the most. And I personally daren't upgrade a physical server (I can recover the VPS...).
I'm actually really keen on Plesk 10, but probably cause I don't use it much, I see the logic in the changes they made, and some of the additions suit our requrements, I'm less than impressed with a quarterly release cycle though! But as it stands its likely we'll offer it as Centos 6 VPS option and I'm unsure what we'll do about shared hosting (the biggest problem with moving to Plesk 9 or 10 for shared hosting is the backups situation... in 9 they take down servers when you download them, in 10 they dont' work!).