this is a very marmite topic... think its even come up a few times on SCN.
a friend of mine has owned turbo motors for years (integra typre r turbo'd, nova turbo and now has a skyline twin turbo) and he agrees in part about flushing engines.
he says doing it all the time is harmful, but once in a blue moon is fine. he flushed his skyline after it landed in the UK.
i had mine flushed, because it hadnt been changed for a while and i went with thicker oil. since then i have had no issues at all with flushing.
each to their own i spose!