Forum OpenACS Q&A: some good recent OpenACS hosting experience
I've ended up with a shortlist made up of:
zill.net (one single aolserver instance on solaris zone), acewebhosting.com (vserver package on red hat/centos) and hub.org (vserver package freebsd).
They all provide vserver accounts for around 40$ a month.
I went in the end with acewebhosting, so I'll outline my experience so far. They seem a bit slow to respond to queries (e.g. not as quick as hub.org for example) although within a reasonable timeframe (same day)
The set up took a while in my case, as a new server had to be rebuild I was told. Once that was done I had a fully working installation of Open ACS. What impressed me was the access speed, much faster than my previous vserver provider here in UK (http://netservers.co.uk/ - in my list they have won the tag "avoid" - slow access, sloppy support)
They also provide some system managament: Server application (OpenACS, Apache, PHP, MySQL, PostgreSQL, FTP and Mail server) installation | General System Updates | Firewall Management | System "Root Kit" Scan | Kernel Updates | Process and Socket Audit | SSH Hardening | Mod_Security Installation/Configuration
All in all acewebhosting win my recommendation.