20 limits on (parts of) main roads in Oxford - several have been done in high ped areas (Summertown, Cowley Road, Headington, Brookes Uni). The County have gone for "naked streets" in those areas (with the exception of Brookes), to the dismay of quite a lot of cyclists. They've proved safe enough, but they're not at all "easy" to cycle along. Virtually all cyclists ride in secondary, regardless of the 20mph. General (but not unanimous) conclusion is that the County should try putting narrow cycle lanes in, and see if it's better or worse.
All of the city centre is 20mph, including the approach under the railway bridge, all the approaches to The Plain, and all the main junctions in the centre. Including St Giles (!). Compliance is variable, but you can mostly get away with pulling out without looking: you certainly won't get much abuse.
Every single side road is 20mph & compliance is pretty good. Still the occasional idiot. You can mostly wander about in primary without getting abuse.
But actually I think it's more notable that the 30mph limits on the rest of the main roads have almost total compliance: that's what comes (in my opinion) of consistently cutting down the width and/or forward visibility. You can't wander into primary or turn right without looking (or sometimes at all), but you can cycle around in secondary without too much stress.
Re Botley Road - the awful bit on the pavement outbound was done before we knew about set-backs etc. There's a cunning plan to sort it out, funding permitting (which would make a bus/cycle lane on the road, and a separate slow route on the pavement). Similarly we're not happy with the north end of Woodstock Road - it's ok for slow cyclists, but not good enough for the fast commuters. A lot depends on quite how little width you can get away with giving cars (and buses). The County are far more open to sub-3m widths than they were 10 years ago.
I don't accept that divvying up the road is barbaric, otherwise we wouldn't have pavements. What's barbaric is people using a road purely as a link, with no consideration for it's role as a place. Given the press of traffic, I think you can only make them respect "place" if you give them a defined, and deliberately tight space.