For the most part, I'm content with MKII and wonder if it is really worth
the effort to move to MKIV.  Perhaps the sample is skewed, but after reading
the mailing list I get the impression that the current experimental/beta
MKIV has a number of bugs and is not particularly feature complete when
compared to MKII.

My current suggestion is that if you find MKII adequate for you use, do not switch now. Wait until things stablize a bit, or you need an exotic feature for which is only availble in MKIV, or you want to help with testing MKIV.