jamroom can be 5 anywhere from extremely easy to use if yo have a simple design in mind and basic needs, to very powerful, but requiring some skills to set up.
a basic site for instance you simply install modules and skins and in quota config grant access to all quotas (you are likely to use only 1) you then can use the skin style editor to make basic changes like colors and font sizes
this anyone can do easily and quickly
but that does not unlock the full power and potential of a jamroom powered site
when i came to jamroom i was confused and lost, and i had a fair amount of web design experience, just never with this template based smarty code type sites. it took a couple weeks to really dive in and become comfortable, but then i saw the full potential of jamroom powered sites.. when you can change the default display behaviors by creating custom templates or editing existing templates.
the quota systems powerful as well take my new site as an example (only been up a week or 2 so not very active yet) www.freedomswings.org notice the members are divided into quotas like glider pilot students instructors pilots board members etc this lets you list members, or members content by quotas, grant quotas access to some modules and not others, show menu items to some quotas and not others. like only board members can post events in the general events calendar
now that you understand quotas (member types) design is next
you create your site using the sitebuilder or use the layout defaults from the skin
if sitebuilder you can use default templates for modules or create your own
you can edit skin, and even module templates directly, or create custom templates from scratch (like i did on www.dreadlockssite.com for index page forum listing blog list, music page list video page list etc) this alows you to use smarty codes in powerful ways like building urls by filling in data for jamroom base url (your domain) user id module item id item title etc and "call in" modules that arent normally included like adding ratings or like buttons to comments
lastly to really unlock the design potential, editing the css files directly gives you far greater control then the built in styles editor does..
so to summarize, jr can be simple enough to throw p a fully working site in an hour, or powerful enough to require some skills but allow you to build your site to your exact needs and specifications, making it look any way you want (to the point that after designing the site its nearly impossible to tell what skin was used to begin with)
if you need help let me know