Ok, I have been using the Jet JJ-12 jointer for about a year now. It is a wonderful jointer. I don't have any other jointer experience, except with my friend's 4", so I am by no means a "jointer expert".
Here are some of my thoughts, recommendations, upgrades, etc.
1. Upgrade - The 4" dust port had to go (See Photo #1). Even with the cleaning and waxing, wide boards created too large of chips and the chute would clog. Every couple of boards, I would have to remove the hose and stick the piece of oak, you can see in photo #4, into the chute and remove the clog.
I removed the complete pan and port. I replaced them with a 1/2" x 15.5" x 20" plywood that I had mounted a 6" diameter HVAC (Lowes) port on (See Photo #2). Much to my surprise, the HVAC port accepted a 6" O.D. coupler. Temporarily, I ran a 6" flexible hose to the JJ-12 directly from my Jet DC-1100 to see if it would work. It worked great! I had an extra 5" flexible hose that I ran from my Top Hat Separator and I have had no clogs since!
2. Recommendations - Keep the simple maintenance on schedule and the JJ-12 just keeps on working. I had set the tables for level and cross-level when I first got the JJ-12 in my shop. They were out a little bit from the move. One bolt needed a 1/4 turn on the in-feed table to be perfectly in line. Periodic table waxing or applying the Dri-Coat stuff, keeps the table nice and slick for those 6" x 8" x 10' timbers that I have been jointing before resawing.
3. Thoughts - I am really glad that I purchased the JJ-12. It is well made and will probably outlast me. I don't see how I could have gotten away with less than 12" width. I sometimes wonder if I need to go to a 16". I have 600+ bdft of rough cut maple that is waiting to be jointed, re-sawn and planed...many of the boards are wider than 12", which means that I will have to first saw them to fit the JJ-12 and then probably glue them back together for table tops.
Here is a sample of the lumber that I have used on the JJ-12 so far: myrtle wood, douglas fir, philippine mahogany, flowering plum, maple, oak & cherry.
If you have a Jet JJ-12, please post your comments. Maybe we can get some enthusiasm going for the JJ-12