It really depends on the species of anemone. BTAs, which are typically the most common in reef tanks, are notorious for moving around, and are one of the only anemones that inflate like a balloon and float around the tank, inevitably into a powerhead.
There are some anemones that are well suited for reef tanks, with some caveats. For example, H. magnifica (AKA Ritteri) are great if healthy when acquired, and if given the proper environment, they typically stay in place (a flat rock away from tank walls--forming a rock "island"--so that they can spread their foot our like a fried egg, as well as ample light and flow). They're also natural hosts to both percula and ocellaris, which are typically the mosts common clownfish species in our reef tanks.
