drupal, like any software package, has flaws that need to be fixed. with a commercial product, however, someone is responsible for seeing that problems are addressed and the customers are kept happy. because OS has no customers, and no company per se (something i think is great, in general), the pressure to keep anyone happy is missing. the various module suppliers are the ones responsible for customer service -- and frankly, most of them could appear to give a rat's ass.
massmailer, for example, has a bug. it's a little bug, but it's affected a few people, including a guy named John Jonas, who, being a php programmer, spent a few hours looking at the code and finding the problem. one line of one file was missing 2 periods, and with that taken care of, MM worked for him -- and for me. (of course, i've reported this bug appropriately.)
the point is that this problem has existed, it's been reported, and it took an outsider to find the bug. meanwhile, people keep trying to use MM because the drupal "community" says how wonderful drupal is, how superior OS is to commercial ware, how responsive people are to your problems, bla bla bla. except problems go on and on, and if a developer feels like fixing the problem, great; if not, tough. newbies are made to feel like idiots, and if unlike me you don't have a programmer pal to turn to, you'll waste hours and weeks on something you are told is a brilliant solution -- that fails.