The brush needs to be tight to do its job. You realy shouldnt have to much creosote buildup after one season, i burn 3-4 cords a year in my epa appliance and i get about a 8oz jar worth of creosote.
A link to the photo:
http://www.hearth.com/econtent/index.php/forums/viewthread/1598/
If you truly have that much deposit you need to work on your technique a little. If you poke around the link i sent you you will find tons of data. hearth.com seems more geared to woodburning then gardenweb, were most of the threads deal with gas appliances. My guess is your prematurely choking the fire down. Any way, ACS is a good product. Get some flexable rods, tie rope on the end loop anyway just incase you come unthreaded in the flue, and scrub it up and down. Nylon has to work hard to clean hard creosote, thats why its tough to get into that liner.
If you had a chimney fire, it can ruin your liner. Your liner is there for two reasons, one to keep your house from burning down in the event of a chimney fire, second, to assist draft with a efficient appliance.
I will say again, there are some real liner pro's at hearth.com, if you dont feel like posting, just use the search feature and you will find tons of info on liners and cleaning them. Hope that helped.

Thanks, Mountainstoveguy.... good answer. I saw the picture of the glass of your own creosote build-up on the hearth.com site.

Now that you mention it, I believe that I was choking the insert too much, too soon last year. This increases the burn time, but then increases the creosote build-up.

I have a round Rutland burn indicator on top the top plate of the insert. It was usually in the "creosote" zone.... or just in the low burn zone. How can one get the temp higher? Do I just run it full open, when the temp gets up in the burn one, then choke it down?

On an initial look, hearth.com looks full of information. I'll dig into it further. Perhaps I'll post there.

One more factor is the wood, if your burning not so dry wood it will also creat creosote no matter what your technique is. As a rule of thumb, if your chimney is emmiting smoke, then its forming creosote. You would expect to see smoke at start up and when you add fuel to the established fire. other then that you should not see any smoke.
I fill my firebox with wood when the stove is cold, and let that burn full open untill i have a charcoal fire that is extremly hot. Then i can add a log and choke it down about half way and still get clean combustion. From that point on, i can load what i want, and as log as i let it get going real good, i can choke it down. I rarley choke it all the way down unless i have a inferno of a coal bed. My glass and my chimney stay clean with this method, it cost me a little bit more wood, but im extracting every btu out of it when you dont let the smoke go up the chimney, smoke is a fuel too you know....

call a chimney sweep. we use flex poles to get down the flex liners. pay the $100 bucks know its done correct and theyare insurred you aren't for those types of mistakes.