I can sympathise with Mike's frustration at his Northern Wheatear the other day when Dave B trumped him with a Desert Wheatear on Skomer. By my reckoning (reference to Birds of Pembrokeshire & Birding in Pembrokeshire), we have had 7 rare wheatear records and all of them have been on the islands: Ramsey (Pied), Skomer (Desert & Black-eared) and Skokholm (Isabelline, Pied & 2 Deserts). No doubt observer coverage is an issue as there should be no reason why one shouldn't occur on the mainland, for instance the proportion of mainland Yellow-browed Warblers to the islands is clearly in the mainland camp (habitat perhaps helping here).
It's also worth pointing out that this prolonged run of south easterlies continues to produce birds you wouldn't expect at this time of year, or some species in very high numbers: e.g. Red-rumped Swallow today (Norfolk), Sharp-tailed Sandpiper today (Avon), Temminck's Stint yesterday (Devon), influxes of Desert Wheatear, Hume's Warbler, and grey geese (especially Tundra Bean & European White-fronted). Get out there - the autumn is well and truly still alive!