Hi, I too have the 6600 and really love it.
As for how often you need to clean the bobbin area....it really does depend on what you are doing and what you are using.
I discovered Aurifil thread a little while ago and have been pleasantly suprised at the very low lint it produces, but then some of the fabrics I use can in themselves produce a lot of lint.
To clean just unscrew the plate with the funny triangular metal screwdriver...it fits under the machine much easier than the normal screwdriver, pop the bobbin race out and use your lint brush. sometimes I just run the brush attachment on my vacuum over it to suck out anything deeper......a word of caution here, make sure you have put the screws somewhere safe....it is a pain trying to get them out of the vacuum (don't ask how I know !!!)
I tend to clean often to keep the thread cutter free of lint as I love that feature on the machine.
The only issue I have with the 6600 is the paint quality. I tend to put everything on to a scrap of fabric rather than on the machine as it does tend to scratch easily.
As for the lock stitch button ...someone else has answered that perfectly....I do however use mine most of the time and never have a problem with a stitch coming undone.
Hope you have great fun with the machine....It took me a while to get used to mine having used Husqvarna Viking and Pfaff before but I wouldn't change it now for anything. If ever you get a tension problem especially when FMQ just press the up/down needle button....it resets your tension and works brilliantly.....happy sewing
Last edited by Little RoO; 06-05-2012 at 12:33 AM.