I have a 1000 on my 65g (36x18x24) and two 1500 on my 120g (60x18x26). They are a great budget filter and with on-line sales you can get these for pretty cheap. You will need to buy some bio filter media however because all they provide is carbon, sponge and white pads.
You will want to over filter with these, like it was mentioned already.
My 1000 on the 65g is very lightly stocked with 6 little fish about 1.5" in length (4 Buenos Aries Tetras and a pair of Blue Eye Cichlids). This filter is more than adequate for this. When I was using this as a grow out for the fish in my 120g, I could see the need for a bigger filter.
My 120g that uses the two 1500's at times even feels under filtered with: 6" Midas x1 , 5" Red Hook Silver Dollars x5 and a 5" Pleco x1. I do 3 water changes a week of 30g because these guys are all messy and poop a lot. But all in all I'm happy with these filters ability.
Just an extra thing to think about: One thing I did do when setting up the canisters was to ditch the in tank heaters. Its a great time to get a Hydor in line heater. Best $45 Ive spent. Get those stupid looking, breakable heaters out of the tank.
All this ranting and I never really made my point!
Cascades are great filters for those on a budget.