I was brought up in Ireland, and my brother, who takes a keen interest in linguistic matters, says he's almost certain that the use of the "t" sound in words like "third" and "three" has become more pronounced in recent decades. It's particularly noticable in the speech high-profile Irish bands and celebrities.

It's an observable phenomenon that when a region or colony becomes independent from a mother-nation/coloniser/oppressor (however you like to put it), the speech and accent in the newly independent nation tends to veer away from the earlier speech-patterns. If you listen to broadcasts of US or Irish politicians and public speakers from, say, the middle of the 20th century, you'll notice that their accents are often more English, and less American or Irish, than they would be now.

So it's quite likely that speech habits like dropping the "th" sound, which probably originated in gaelic-speaking areas, are becoming more standard throughout Ireland (or at least the Republic), for what might be called politico-linguistic reasons, even in the speech of people who speak only English.

But pronouncing "thyme" and "Thames" with a soft "th" is just being perverse, or taking the piss, if you ask me.

Marje