Here's my own stance on the retro-clones. As I've said a few times in this blog, all they really boil down to is glorified shibboleths. I don't believe that they provide a solution to an otherwise insurmountable legal problem with publishing 'unlicensed game supplements'; that problem almost certainly doesn't exist. Nor do I believe they are necessary to preserve the older versions of D&D - all of which are available to buy as pdfs.
What they are useful for is as a means for like-minded people to easily identify one another. "D&D" will generally always mean the current or latest edition of the game to most roleplayers. At the moment, it's synonymous with "4th edition D&D". Fine, no problem, that's the way the world works, whatever ones personal likes and dislikes might be. But it does mean that saying "I like D&D" is problematic for someone who likes older editions. Other people might get the wrong idea and assume you play a game involving 'controllers', 'daily powers' and half-orcs with origins that absolutely do not involve anything bad.
However, say the magic words: "Swords & Wizardry", "OSRIC", "Labyrinth Lord", and if anybody within earshot is 'in the know' - Bingo! - they'll identify you as somebody who probably shares a similar gaming style. And vice-versa. Love, or at least mutual satisfaction, (ahem) will blossom. What's more, saying "Swords & Wizardry" has a kind of cache that saying "I like AD&D" or "I like B/X D&D" doesn't. It immediately lets the right kind of person know that you are in the club. Probably you read all the blogs and forums that the cool people read, have the right playstyle (sandbox, megadungeon, 'rulings not rules'), and possess a healthy disregard for Wizards of the Coast. You are one of the special ones, and all the other special ones will identify you as one of their own. This is a nice feeling to have. Belonging. And a hint of superiority over 'ordinary gamers'.
Nothing wrong with this of course - it's natural human behaviour that we all exhibit, no matter what hobby we have. In my circle of friends in school, saying that your favourite Smashing Pumpkins album was Pisces Iscariot had much the same function - it meant you were in the know, and to be trusted as somebody with impeccable taste. More usefully, the Flemish used to get people to pronounce the words 'schild en vriend' as a means of rooting out French speakers, who would pronounce them 'skild en frend'. And be killed.
Also, I should point out that I like Swords & Wizardry a lot as a cleaned-up version of OD&D, so no complaints about it on that score. But let's stop pretending that it's all just a way of getting around a legal problem now, shall we?
EDIT: Somebody in the comments to the post at LotFP makes the excellent point that the retro clones are free. Also, they are presented better than the older editions. These two factors make them excellent tools for spreading the word. But hey, I have broken ribs and have been writing