There is a very well known engineering/production axiom: "Cheap, fast, good. Choose two." In terms of a product like this you could pose it as "Cheap, great spec, good. Choose two."
It's a very cheap product made down to a price both in terms of materials/components and quality assurance. The most obvious physical manifestation of this to the user is the incredibly crappy headphone socket which has several problems: it is not always soldered securely, it's very short so only holds a tiny section of any jack plug, and it doesn't have the usual spring clamp so doesn't securely hold an inserted jack plug.
Having said that it is possible to open the case without breaking internal components. My 8GB Clip+ got immersed in sea water. I opened the case by using a common pry tool like this one
It's easy enough to do and there is no reason to damage anything internal. I did put a small crack in the case outer at its thinnest part, around the microSD slot, and this might be hard to avoid. I rinsed the whole thing with fresh water and left it to dry for a couple of days. It booted! I put the case back together and it has been working for the last 5 months just the same as it had since I bought it in December 2010. "Just the same" in this case means noise from the headphone jack as the unclamped jack plug moves, noise from disk access or CPU load sometimes even during playback, occasional crashes on USB connection and sometimes tracks skipping to the end.
This isn't a Rolls Royce and they don't ask a Rolls Royce price. I think build quality and performance are in line with the very low price. For the price the feature set is very good indeed so you get a lot for your money but nobody should be expecting high quality components throughout, immaculate assembly, or a QA process that enforces standards that the manufacturer isn't even trying to attain. If you get one whose headphone jack is solidly attached and which holds tight to any jack plug, and which doesn't make weird noises and which never hangs then well done. Otherwise join the club of people who got what they paid for.
Despite any issues or potential issues I'm not sure there is anything else worth getting for the same price so Sansa have pitched this with great expertise. Despite making some negative comments about the Clip+ I think it is good value, this being validated by a very reliable mechanism, the market itself: it's not a perfect product but you can't get anything as good for the same price and if you want something better you do have to spend more money.
When I don't need the Clip+'s micro size I'm still using my iRiver H140. It is
really nicely built, made of high quality components and has an impressive specification. It is easy to disassemble and reassemble. It sounds better than the Clip+ (noticeable with with higher impedance 'phones and at high levels). It has lasted maybe 8 years so far (two new batteries). Other significant difference? It cost about eight times more than the Clip+.