Roomba? Do they work? Are the more expensive models worth it?

So I'm starting a new job in January, which will mean working two evenings a week until 6:30 or 7 (as opposed to until 4:00 now).  I'm seriously thinking about getting Roomba (or similar off brand) that I can set to run each day while we're at work/school.
 
Do they work?
 
Are the more expensive models worth it? (like they say "multi-room", for example - will the lower models only do one room??)
 
We have a small dog - 15 pounds, half rat-terrier, half Jack Russell.  She sheds, but it's small, fine hair.  I'm also hoping this will help my allergies (dust, mold and mildew are my biggest triggers), so I'd probably pay for the Hepa filter version.
 
Thoughts???

 

I have a love hate relationship with my roomba.  I have a very open floor plan, so open in fact that other than in my family room, there is no way to place the virtual wall since it is either to long to reach the wall, or it only blocks one way not the other.
 
I have 2 dogs, roomba pushes the dog hair in the corners and edges.  So we still have to vacuum.  Because of the layout, roomba gets stuck, so i can't run it when we are not home which kind of makes it less useless that i had hoped.

 

We used to have a roomba before the kids - for about 3-4 years. It was somewhat useful, we used it between vacuuming - it's not as good as a regular vacuum - and we used to find it stuck under a couch most times. After the kids started crawling they were fascinated by it and wanted to climb on it - so it broke soon after. We didn't replace it - thinking the kids will break it again anyway. We don't have any pets - so not sure how it would work for that, but I think pets would like to climb on it also. I think we used to vacuum less often when we had it, so it made a difference. It picks up crumbs and any surface mess - but not the dust in the carpet. If you have hardwoods and an area rug on top - it can get stuck on it.

 

I should have mentioned we have about 80% hardwood floor.  Only two rooms with carpet, and those are Berber, so not thick or fluffy carpet.  We only have a couple of rugs.  So it might be useful for us?  If it cuts my need to vaccum from 2-3 times a week to once a week or so, I'd be satisfied.

 

I mostly use my roomba on tile and hardwood. It gets stuck on the lip between the 2 and the bottom of my bar stools.

 

I love mine. Its a 640? maybe? not sure. I have all hardwood and tile floors on my lower level with rugs at the doors. I've never used it on my carpeted upstairs.  I don't expect miracles from it like getting all the dust bunnies but it helps a lot. I use to vacuum a couple times a day because with all my kids/animals running in and out I had sand throughout my house. I hate walking on sandy floors.
The only thing it has gotten stuck on was a string that was hanging off of my daughter's backpack. Otherwise it bumps into something a few times and then moves along.
It also cleans the sand and dirt off my rugs really well. My rugs are so bad I can't stand to walk on them and after the roomba goes through they are fine.
I've also had issues with hair wrapping around the brushes but all 5 of us girls have really long hair and my regular vacuum has the same issue.
My lower level is about 1600 sq ft and i let it clean everything. It doesn't always get through the whole level before it needs recharging but I just run it later if I need too.