So... reporting back after using the Ultimate Dust Deputy with my CT-36 a bit - I'm pleased. It does indeed collect virtually everything in the plastic bag, and I don't see anything in the vacuum's bag or on the filter. I've done a fair amount of drywall work with it, as well as some general sanding and cutting - and it seems like a good purchase. I see no noticeable loss of suction - though on that I defer to Peter Parfitt's wonderful testing on it showing a slight loss.
I DID experience a significant loss of suction at one point and immediately thought I had damaged something... no, I had just sucked something big in the hose and had it stuck in there causing an almost complete blockage. Once cleared, all was fine.
I was at a Festool Roadshow yesterday and, when asking about the upcoming Planex Easy, mentioned that I was using the UDD on my CT-36 - the Festool employee was not pleased and cautioned me about it. Despite Oneida's work on the UDD, I don't think Festool is too happy about it being used on their dust extractors. I have a couple of big drywall tasks ahead (finish the kitchen, and two bathroom remodels), and some truly obnoxious popcorn ceilings in my house that need to be dealt with - hence the Planex interest. The cost differential between the Planex Easy and the regular Planex would push me into going with the more capable current Planex, I think...
I DO find the UDD/CT-36 combination obnoxiously big, and it makes moving the CT-36 down even one stair level a drama-inducing event; nonetheless, I am pleased with the purchase, would recommend it to others, and will continue to use it. If I DO have issues with it in my remaining two years of warranty, I will fess up to Festool and pay for the repair.
Larry