It's easy to use for easy things. Fortunately most of what I do is easy. It's harder to do harder things but in most cases it is possible to work within the constraints of the system. The documentation is pretty good once you figure out where it is. Support is excellent. I have used Bamboo for several years now and each time I have had to get Atlassian involved in a support issue they have been very helpful. Perhaps once, I've gotten a guy that I knew more than he did.
The bottom line is that if you can script it you can do it in Bamboo. Love the integration with JIRA and Fisheye.
The organization of the gui is meh. I have a lot of plans and spend much of my day scrolling down to find the build or deployment I need to engage. This is particularly true of deployments since there is no "project" grouping mechanism as there is in the build "side"of Bamboo. Deployments functionality is getting better though it still has room for improvement. The documentation on Deployments is still lacking to a degree and the REST API for deployments could improve. I'd like to see more ability to report on activity. How many builds did I do over all during the last x days. How many deployments did I do over the last X days. What is the break down by environment. Get a rest link to the last build log file (this may exist, but I haven't found it in the documentation yet).
I wish there was a mechanism for prompting users for variable values at runtime. And to display build execution instructions (or deployment instructions). These are the only things that is are real hindrances to me.
Set your expections and identify resources. Bamboo can do anything Jenkins can do as far as I know. You get the added integration benefits from other Atlassian tools. The tool isn't the thing though. It is the knowledge of your developers, configuration management users, and operation people who will make your Bamboo implementation successful. Bamboo at it's most basic is a scaffold onto which you add the pieces of your build. You still need to write the scripts that make the objects move around the network. You have to know how to build your application and how to translate those instructions to the plugins that you use in Bamboo.
Build and deploy.
Prior to moving to Subversion from ClearCase and from a manual (somewhat scripted) build process to Bamboo the build process was exceedingly long and difficult. We've sliced the build from 3-5 hours to fifteen minutes in most big projects.