I bought my QE 4.0 in 2011 (Wow - 4 years). I know I have not used it to its full capabilities. I have had no problems. I love the longer throat (at that time Bernina had not come out with it yet.) I have done regular straight sewing, some of the "fancy" stitches. I am still trying to learn FMQ. I have encountered none of the issues others have described. The IDT is wonderful as is Needle Down. I have a great dealer and am confident any issues would be resolved.
I chose the Pfaff when I felt my Bernina 707 from 1973 no longer filled my needs. I compared the Bernina and Pfaff. The longer throat is what really sold me.