Forum OpenACS Q&A: Is a shared and managed hosting option avaialble ....
The hosting options that I have got so far with openacs is either a virtual machine dedicated hosting or dedicated hosting .
Looking forward to find such a web hosting service ...
I think Patrick of Zill.net offers shared. You can look at the community page for hosting options
I would recommend zill and acorn, I had very good experience with them. They are nice small shops and the level of service is still personal and prompt. I had a bad experience from a mid size shop. I did have good exprience from bigger size shops like Globix, although I don't think they will offer shared hosting of OpenACS. Good luck.
The limitation is that the service I use is really for low/medium volume sites, but it would be worth asking about your specific requirements. Cathy Sarisky is very responsive.
For me here's not much admin involved, except vacuuming the db (and if you use a 7.4 Postgresql, the pg_autovacuum in contrib fixes that) and backing up (for which a number of automated solutions are well documented).