Must say it's a little worrying reading about this issue. I guess the advice ought to be to simply avoid using the headphones socket! Out of the question for some perhaps, but I would point out that bluetooth headphones/headsets are actually very affordable now. £20-£30 gets a fairly good pair of headphones, which will render this issue kinda harmless (if usage of the socket is indeed the culprit). Plus, who wants cables trailing out of their mobile phone anyway? Unless you absolutely need to use the onboard FM radio, you may as well just leave the 3.5mm socket alone, especially if there's a risk of breaking the earpiece speaker.
Despite this minor issue, I think the Defy is an awesome android phone, and highly recommended. Perhaps in the coming weeks Motorola will acknowledge this problem and sort it out completely - fixing the jack properly for future production, and maybe offering free bluetooth headphones to those who've bought a Defy with this weak socket/earpiece speaker issue (well it would only be fair, certainly cheaper than furnishing all early customers with new Defys... or would that seem to be a far-fetched dream? - help me out, I've no experience with Motorola's aftersales support! Lets hope they feel obliged to do the right thing for all of us who've decided to go for something a little different to the iphone/bberry/htc crowd)