There is a trend towards diphthongization of "ij" that has been going on ever since the 1960s. Actually, back then, "educated" Dutch had ij as an almost pure vowel, and sounded much like educated flemish. IJ as a diphthong has always been part of city dialects. In Rotterdam for instance, it's pronounced "aye" almost. The last couple of years there have been lots of complaints against over-diphtongization of ij, which is considered vulgar and provincial, but it's a tide that can't be stopped.

Informative article about "Polder Dutch"
http://cf.hum.uva.nl/poldernederlands/english/lin_polder.htm

Fascinatingly:

"Stroop (1998) claims that the change is typical of (relatively) young, highly educated, progressive Dutch women, who wish to make a statement through speech that they are unconventional and emancipated. The variety is often found among women with high-prestige social positions such as authors, actors, film producers, artists, left-wing politicians (either local or national), high-ranking academics, and pop-singers. It is for this reason that we prefer the use of the term 'avant-garde' Dutch for the new variety, rather than Polder Dutch, which in hindsight seems a misnomer. It should be pointed out here that the avant-garde variety is found throughout the country. It is not based on any existing dialect of Dutch, and it has no documented geographic epicentre. So, avant-garde Dutch truly qualifies as a sociolect rather than a dialect or regiolect."

Philip Bloemendal, a model for old fashioned Dutch pronunciation
http://www.youtube.com/watch?v=8bH88ZyKCmw

Katinka Polderman imitates Monique Smit
http://www.youtube.com/watch?v=5PAwkvA9PTc

Well I hear just a normal Dutch pronunciation, both of zijn and pijn. It is a difficult sound for foreigners to get right as it really is a cross between pain and pine.

I've lived in Haarlem for about four years in different stints going back to 1975. I was taught that ij is pronounced like long i or y. For example, dijk is pronounced almost exactly like its English translation dike and ijs like its English equivalent ice.

The combination ij isn't sure whether it's a y or just an ij. In dictionaries it sits between ig and ik. But in modern usage, such as in telephone books and street indexes on maps, it is equivalent to y.

Another quirk of this combo is that if it begins a proper noun both letters are capitalized, as in IJmuiden, a city on the coast of Holland, and the river Het IJ going through the middle of Amsterdam.

In print the combo often looks like an umlaut u, ü or Ü, with a gap near the bottom of the left vertical.

There are regionalisms in the Dutch language despite the fact that it is such a small country. You might look up the birthplace of this singer. He might be Flemish.

spaarne and itsmij, i beg to differ: it's clearly audible (but maybe i've just taken too many phonetics classes) that "old fashioned" ij, is far less diphtonhisized than present-day "ij" . Daniel did pick up the difference between Boudewijn de Groot singing in the late 1960 and present day pronunciation of "ij" just fine.

As illustration, Boudewijn de Groot singing in recent times: a marked difference.

http://www.youtube.com/watch?v=1YNW7KAIRfE

And Rob de Nijs from the early sixties.
http://www.youtube.com/watch?v=j_JWku2yHqc

ritme van de eenzaamheed.

And as a further complication, the city dialect of The Hague, both the low class and the posh variant, is known for the fact that it has "ij" as a pure vowel.

http://www.youtube.com/watch?v=PBBlqDZG9RE

Where I live (edge of het Gooi) many people still say it like in the song, even young people.
It really depends on the local accent I think.

Menachem-- Thank you. I didn't think I was imagining things. I enjoyed your explanation... I can just picture some language traditionalists getting very upset about the diphthongization and drifting toward "polder Dutch" (if I understand that term correctly), kind of like my grandmother found it very uncouth how people stopped pronouncing the "H with the w" in "white", "where", etc... I'm going to check out the Den Haag video now.

hetismij-- I tried to find a modern clip with lots of IJ to give you a sense of what I meant and the difference with Boudewijn. When Nick & Simon sing (1 minute or so in) "zijn" "luistert naar mij", "voorbij", the "ij" is much more like "eye" than the "ai" in main. I can't even make their "ij" into "ai" if I try, while Boudewijn when he sings "pijn", it really sounds almost like "pain". Thanks for offering up your experience, it seems there is a regional component.

http://www.youtube.com/watch?v=XIh8c46E4TE

spaarne-- Boudewijn de Groot, while born in Batavia (now Jakarta, Indonesia) while under Japanese control in WW2, it seems lived mostly in Haarlem and Heemstede, Noord Holland.

As to that last bit of information: there is an Indo-Dutch accent of standard Dutch. Not the "petjoh" Indo-Dutch accent caricature, but something one might call a very correct Dutch pronunciation, with softer "g", and less diphthong in "ij".

Menachem-- I think what just blew me away the most was to listen to that more recent recording of Boudewijn de Groot. His "IJ" seemed too to have morphed into the modern "eye"-like sound. It's fascinating that the same person's pronunciation would mutate in a span of 30 years. Thanks for all the clips.

There may be an Indo-Dutch influence in Meneer de Groot but I'd be surprised since it seems he left as a toddler. BTW I listened to the video from den Haag and I definitely hear that the "mij" sounds quite like the English "may", although the overall rhythm and cadence seems quite in line otherwise with much I've heard of modern Dutch.

Strange as this may sound since I'm relatively new to the language, I feel like I already miss the "sound" of the language in the older clips.

Thanks to all three of you for the time you took responding.

Indo dutch is the eurasian community inside the Netherlands.

Here's Adriaan van Dis, also an "indo"

http://www.youtube.com/watch?v=bp-isuGQLFg

Often, his accent is decried as being "posh" and affected, but I think his accent can be explained from his Eurasian background. I think there are similarities between his way of speaking and early Boudewijn.