In the recent release of phpBB, one can create RSS feeds for each single forum. If you want to subscribe to multiple forums this way, you have to add multiple single feeds. Thus, global announcements occur multiple times (one for each feed).
Prior mods for phpBB 2.x allowed an extended format for selecting the forums to create a feed of: you did not need to add feed.php?f=1, feed.php?f=2 and feed.php?f=3 to your reader. feed.php?f=1,2,3 covered all three forums in one feed. It would be nice to see this feature in phpBB 3.x