Sekio is correct, MDPV has pretty much disappeared worldwide now for around the last 6 years or so. I've heard rumors that there might still be some in Russia but for the rest of the world it's mostly considered extinct and has been 'replaced' by newer research chemicals like a-php, 3f-pvp, etc
Vaporizing MDPV in a pipe does leave a sticky residue in the pipe and pipe stem. After lots of use there will be enough residue that it can be collected/scrapped out and then vaporized again. It's usually very sticky though which makes it a pain in the ass to work with especially if you've been up for six days, your naked with porn playing on repeat, haven't eaten and believe the cops are about to bust down your door.
To me MDPV is a very special stimulant. It's difficult for me to fully explain why but to keep things somewhat short it just feels good, is very very compulsive and often makes me very horny. Like sekio said, if you are interested in reading others experiences with MDPV then it's probably best to read erowid trip reports or search around as it's been discussed so much over the years on all sorts of places on the internet.
I have not seen the 'Intervention' episode you mentioned but yes, it is quite common for MDPV users to experience these "shadow people". This is not unique to MDPV, it can occur from any stimulant use and is mostly an effect from excessive use, lack of sleep + dehydration and lack of food.
MDPV does seem more prone to things like psychosis and seeing/hearing these shadow people then other stimulants. There are a couple of reasons for this, one may be that MDPV is just chemically more likely to do so in the brain but mostly it's because of MDPVs effects - it's highly compulsive nature coupled with its long duration is just a recipe for disaster unless the user is well disciplined.
Example, A user will take a hit, get a very strong rush and then a little while later will experience a very strong urge to redose in order to experience another rush. This is especially problematic because MDPV is quite long acting, so it's very easy for somebody to use, then use more, then keep using more and then stay up for days and days until psychosis sets in - all the while still using more and more and not being able to stop.
MDPV has a similar rush and compulsion to redose like crack does, so often users will use MDPV like they would use crack: they continuously redose every 20 minutes or so. Once a crack user stops smoking crack they are usually able to fall asleep within a few hours whereas somebody using shit loads of MDPV probably won't be able to fall asleep for another 10 hours after there last dose, maybe even 24 hours if they have used an excessive amount (which is very likely). So getting to a point of excessive use and many days of no sleep is very easy to do with MDPV, hence part of the reason it is so strongly associated with the shadow people.
