Upload & Sell: On
I've never found the bokeh of the F4IS to be objectionable. Nor have I found it soft or low in contrast at longer focal lengths near mdf. I think it is a stellar lens.
The quality of bokeh is greatly affected by the nature of the background. Here's a thread I posted about the funky bokeh on my f/4L IS, which is exacerbated by the addition of an EF 1.4x Extender (Mk I), http://www.fredmiranda.com/forum/topic/948575
I've also compared bokeh from the 70-200mm f/4L IS without extender, with the f/2.8L IS Mk I and II, Mamiya A 200/2.8 APO, Leica Apo-Telyt-R 180/3.4, and Voigtlander APO-Lanthar 180/4. In terms of 'quality, or personal preference, bokeh of the Canon f/4 L IS and APO Lanthar lag far behind the f/2.8's. The Apo-Telyt is in between. YMMV.