I gather that the French, or at any rate a few of their literati, are getting their culottes in a twist about an alleged decline in the use of semi-colons which they seem to believe is largely the fault of the Anglo-Saxons. The Guardian took this bit of paranoia seriously enough to print on 4th April an exhaustive piece about semi-colons; a letter the next day aptly described the row as "an agonised and pretentious debate". So read it if you like, but don't pay too much attention to any of it. It seems that modern French writers like François Cavanna and Philippe Djian are anti, while Proust and sundry Academicians were or are pro; over here, Shaw was ridiculously pro, Orwell was anti, but so what?
Lynne Truss in Eats, Shoots and Leaves provides a clear, witty and sensible summary of the long history of the semi-colon and of its proper use. My guess, not based on any real evidence, is that, in English at any rate, it is less popular than in the last century but is still widely used and is certainly not in terminal decline.
So far this year I have published on the net around 12,200 words, using 65 semi-colons. This is probably more than the average rate of usage by all those who use them at all, which many perfectly adequate writers do not. Perhaps half of these could be replaced by full stops or colons (never by commas except in lists) without damaging the sense or clarity, but replacing the others would, I think, be a pity.
Using a semi-colon just because a sentence looks a bit long and you want to split it up is to be avoided except where the separate parts have a closer relationship than that of sentences which are merely consecutive. It is also usually unnecessary: even a sentence like the first one here would not be improved by chopping it up.
When I looked back at pieces I had written in my twenties I was surprised to find that in those days I hardly ever used semi-colons. It may be that a predilection for the little dears is something that creeps up on you with advancing age, like arthritis, dribbling, and forgetting things.
As you see, I quite like Oxford (a.k.a Harvard) commas as well.