I'm not sure what you mean my 'managed services'. The first thing that comes to mind is that linode would install or configure software within the VM. That seems like a world of hurt, someone can do all sorts of crazy sadistic things to make that be a huge pain in the ass for linode. I don't think it's possible to do other than billing out at the hour.
However, if you me 'managed services' as some additional services linode could offer to make their service more attractive I have some ideas of some services that someone might be interested in, and willing to pay money for. Some are better than others and I'm not sure there's enough users to justify some. But here's a list of possibilities:
1. Mail
This is probably the biggest one to me. I do not want to run mail, and am willing to pay to make that happen. I think linode could offer smtp and a simple web-mail solution that could make things very easy. I would suggest charging per user.
2. Firewall
One of the tasks one most people tackle first node is establishing a firewall. Sure we can use iptables locally on the host, but for those users who don't want to mess with that linode could provide a simple firewalling service.
3. Load Balancer
I'm not at this level yet, but I could see some who might be. They want to load balance between several nodes, and the cool thing is instead of simple DNS round robbin linode could look at things like the node's load average to decide on balancing. Perhaps with this service we could also off load SSL process to the load balancer?
4. Database
I think most people at linode are just running simple web-based application with a database backend such as wordpress or drupal. How cool would it be to use a database maintained my linode on a separate vm. Think how much more oooomph you could get out of each node after off loading the database load
5. Memcache
Not sure if this is really all that awesome, but maybe. linode could run a simple memcache service and hopefully secure it by local IPs. I remember reading someone is trying to provide that service on linode, but it sounded like just some yahoo... not someone you can trust with a client's web-application, but maybe I'm wrong.
6. LDAP
For those who have multiple nodes it would be nice to be able to out-source an LDAP service. Linode could provide a simple web-based interface for managing users, and hopefully it would be able to store ssh-keys in LDAP so I don't have to configure that each time I setup a new instance.
Scott Phillips