Indeed one of the fun perks of the mirrorless cameras is that due to having virtually no registration gap between sensor and lens, they can use just about any lens ever made for nearly any camera ever made, from rangefinder to DSLR to medium formet to video to surveillance. All the adapters need to do is serve as a 'spacer', to set the lens the proper distance from the sensor - so the adapters are 'dumb' - just empty hollow metal rings.
The exception are the more complex adapters that have additional functionality - such as the ones designed for Sony's Alpha lenses where the adapter includes electronic connections for the lens so the camera can set the aperture, and even a larger adapter with a built-in focus motor and one with an entire mirror assembly with phase-detect focu sensors.
If your Canon lenses have no aperture rings on the lens itself, then you'd have to chip in for a slightly more expensive adapter that has an aperture control ring built in - or there are even new adapters for Canon lenses recently debuting that actually have electronic connections that allow aperture control through the camera body! They'll be pricier, but for someone with a nice Canon lens collection, that could be a great thing to have.
As Kathy mentioned, all lenses you adapt from another mount will be manual focus, so you lose autofocus capability. But the NEX cameras have two different focus aid systems that both help make it easier to do so - one is a focus magnification function that 'zooms in' the view to allow critical focusing, and the other is the 'focus peaking' function which highlights the contrast edges within the scene that are in focus, allowing you to easily see at a glance where your focus area is.
The NEX-5N also has an optional electronic viewfinder that can be added, which could help with longer lenses, focusing, and stability, if you prefer putting the camera to the eye rather than using the tilting LCD.
It's that modularity of the NEX system that makesit interesting and useful - you can strip it down to just the tiny body and one basic lens, and have excellent portability, or you can add on flash, more flash, or electronic viewfinder, lens adapter, adapters with focus, full phase-detect mirror assemblies - it can be as big, heavy, and fast as a DSLR or stripped down to P&S size, depending on your needs.