Jeff -
I once owned a JD 185 48" w/ the JD 2-bag collector system that hangs off the rear. The 3-blade deck generated sufficient airflow to push most clippings up and thru the hard chute into the bags so long as I was being reasonable with ground speed. Get going too fast and it would clog (particularly with wet grass) but, after a a little trial and error, you soon get a feel for it's capabilities. I used it mostly for picking up the windrows when cutting after the grass got higher than normal (as opposed to missing a mowing /forums/images/graemlins/wink.gif). That worked better than mowing high grass with the bagger on; the bags seemed to hold a little more after the 'double' chopping. Well, probably doesn't hold any more, but the finer clippings extended time between trips to the dump pile. Same with Fall leave pickup, best to go over 'em once or twice without the bagger, then put it on for pickup.
My take is pretty simple, they do what they are designed for generally, but I think it is more a question of how big your jobs are. I quickly realized the limitations when I was spending more time going back and forth to the compost pile to empty the small bags than 'collecting'. My first 'solution' was to park a trailer nearby on the lawn and dump onto that, then take one big trip back to the compost pile 3 acres away. Saved time and gas, but that meant handling the clippings twice. Took me a few years to see the light and save the buck$ but I finally ponied up for a pull behind 8hp vac trailer. Worth every penny IMO and I never used the bagger setup after (though I kept it when I traded the mower, any locals PM me if interested).
Long story short... if you have a lot of leaves and maintain a larger lawn, I would skip the bagger and go right to a lawn vac if you can afford it. Of course there is an expense to operate and maintain the vac but, aside from that, the only downside I see is storage space.
