Given the surprising lack of a repeat, I made time to watch the first part of Birdsong on iPlayer before it expired. I still have the second part on my Sky+ box waiting to be watched.
The experience proved to be much as I had expected - several times during the show the system stopped while it buffered the next few minutes for viewing. And, somewhat surprisingly, putting it on pause for several minutes didn't help. It seems that iPlayer doesn't buffer any more than a few moments in advance.
But my absolute favourite moment was when, close to the end, just as we were getting to the climactic events that would set up the second part... the system declared that I didn't have the bandwidth to continue streaming, and just stopped. Yay!
In the event, I just reloaded the page, started viewing again, and skipped to the same point as before, so it wasn't a huge hardship. It was something of a pain, though.
As for the show itself, I rather enjoyed it. I certainly didn't have any difficulties hearing the dialogue; I'm not quite sure what all the complaints about 'mumbling' were all about. It certainly seemed to be a rather closer adaptation than either "Great Expectations" or "Treasure Island", which was good. Though I think I would still recommend reading the novel instead.