One is that there was a huge ammount of cultural exchange between the Celts and the Picts.

The Picts as a culture were wiped from the face of the Earth by the Scoti who were a Celtic tribe. The Picti/Scoti later called "Scots" invented the Kilt.
I'm not sure how accurate the second part of the quote might be, Sir Robert. Cairney held that the Scotti were Errainian Gaels who might have been Cruibhne in origin, or intermarried with them before they crossed over to Ireland; he then held that the Dal Riadans crossed back to the Earra-Gaidheal (Argyll) in the 5th or 6th Century. Anyway, the various Pictish kingdoms to the east - such as Ce, Fortrenn, Fib - themselves expanded and Fortrenn absorbed most of them - there was certainly intermarriage between the Scots and the Picts of Fortrenn (and also with the "Welsh" of Strathclyde). Some writers have held that Pictish was a separate 'P' Celtic language: this is speculation, as there isn't enough evidence apart from place-names. But Fortrenn under Oengus mac Fergusso (a suspiciously Scots sounding name) did conquer Dal Riada; and Dal Riada rose again under Coinnich mac Ailpein (a rather Strathclyde sounding name) (Kenneth MacAlpine) and formed the Kingdom of the Picts and Scots. So I don't think the one wiped out the other culturally - I assume that there was a gradual cultural convergence.