I feel like the major consideration is: do you have kids or pets? Then get one. Otherwise, probably not worth it.
If you have small-ish kids, you end up vacuuming everyday one way or the other. A Roomba's a decent stand-in for that. When my kids aren't at home, I mostly get by with my stick vacuum. (There the battery-driven ones really are nice.) With the stick vacuum it doesn't tend to leave my cables and rugs in random places, which makes the daily non-kid-time vacuuming similar levels of effort.
I assume pets are a similar deal, though I'm not a pet person.
One thing that hadn't occurred to me before getting the Roomba is that it vacuums a lot of places I wouldn't regularly get to on my own (e.g. under the sofa), and there's some benefit of having a cleaning session frequently that gets to a lot of those places that are otherwise hard to reach. But again, with kids not at home, I run it about once a week.
I'm genuinely curious about the mopping ones since I don't mop often, and always like it when I do. ;-)