While I was faffing with my phone at work yesterday (and mostly because I had my nandroid backup of the 'stock O2' software on my PC at home!), I figured I'd give ARHD from XDA-Developers a try, as it's based on the same source as the MCR so i wondered if it suffered from the same problems. This ROM doesn't have the FB/Friendstream issue, and worked straight away. This has the latest version of FB installed (1.9.3 I believe?), and isn't causing any problems.
Checking the app list, that ROM too has the same 2 Friendstream apps listed, but also has 'Facebook for HTC Sense' listed as an app. This wasn't showing on the MCR. It is listed as version 4.0.2215172619.345324.334711. Not presuming to teach you to suck eggs or anything, but could it be a simple kitchen issue? The 'Facebook for Friendstream' option was definitely ticked when I baked the ROMs, so could it be that whatever code it is you've written to run the kitchen has just had a flag for these installed items pointing the wrong way? (ie. "if ticked then do not install" instead of "install if ticked"?)
Of course, it might not be that. As ARHD isn't based strictly on stock the way MCR is, you have to do a full wipe and format of 'system' prior to install. I confess I haven't tried doing a full wipe and installing MCR again.
(For reference for others - ARH is pretty decent as a ROM if you like things to look and feel pretty stock, much like the MCRs. The RAM optimisations seem to have worked, as in general use I struggle to have less than about 350Mb of free RAM, as opposed to about 270Mb on stock.
That said, it still doesn't seem as smooth and fluid as MCR did for the brief period I was using it. Don't know which kernel Paul is using for MCR, but ARHD is based on 22.214.171.124.
Once Paul works out what the issue with Friendstream et all is, I will be moving back to MCR - I used one for just under 2 years on my Desire, and it never skipped a beat, hence I trust it. ARHD I'm happy to try, but I don't trust it anywhere near as much just yet.)