I have been using ISPconfig2 for about 2 years and it was/is rock solid, now we have bigger needs and we are rolling out multi server environment with ISPconfig3.
Multi Server function is THE reason to move from v2 and other things like virtualmail users, language editor and that you can have separated email hosting packages as well webhosting packages.
We are rolling out ISPconfig3 as interface only on one server, than we are connecting webserver/db, mailserver and dns servers. They are all separated servers. Behind that we have san storage and bacula backup solution. All this is runing on Debian Lenny 64bit.
We are still in testing period and if it continuos to work as good as now we are deploying the new hosting solution next month. All this is possible with the new ISPconfig 3 and as you can see there is huge advantages with the new version.
Than again if you don't have many clients than you can stick with v2 but i think that more users should move to v3 so the dev team can fine tune v3
ISPconfig community with the developers are just awesome, thank you so much for this nice piece of software. You guys deserve all the credit