Had my first encounter with the mexxy lady this week. 6'7" male 235 lbs 13% bodyfat (lean, muscular build), 23 years of age. Previous experience with drugs includes extensive use of all the classical psychedelics, along with many different synthetic phenethylamines and tryptamines, and ketamine. No experience with opiates or amphetamines so I can't comment on similarities or differences in that regard.
I insufflated mexxy three days in a row, but only once per day with no re-upping. First day was 50mg; second day 25mg; third day 75mg. This was done purposely and not compulsively, and daily use was discontinued without problems after three days.
Pros: From a psychonaut's point of view this thing is a goldmine. It's no wonder to me that this substance has achieved the status it has so quickly. At sub-hole doses and without combining, I found the high to be lucid, empowering, clear and insightful with no anxiety. At more dissociative dosages (75mg), High appreciation for art--the film is experienced as an "audio-visual" poem. Very productive compound for writing; the mindstate is lucid but free and unattached, with a diverse array of normally sedimented or otherwise imperceptibly enveloped interconnections deterritorializing and offering themselves over to codification. Articulation and insight into reality is optimized, though of course various feedback loops and the sense that one's thoughts are moving too quickly to record restrict the efficiency of codification. It is, however, the very experience of the offering-over to codification that sticks with me, into the proceeding sobriety where it is the business of psychonauts to reflect and integrate. Effects began inside of 10 minutes. The effects came on strong but the intense and unpredictable acceleration of effects stabilized at about the half hour mark, followed by a steady climb to peaking at about the hour mark. Heavy time dilation and dissociation. Body load is pleasant when seated, no anxiety. When moving about gravity plays tricks. This latter effect is great fun so long as you don't feel any pressure to 'appear' sober.
Cons: It's reasonable to believe there may be a neurocorrective mechanism in dissociative like mexxy and ketamine, with noted anti-depressant effects occurring for days after use. However, I found that after three days of use in a row, mexxy had shown herself to be quite narcissistic, a quality that simultaneously lends to a drug an intense and robust personality, but also a danger of turning around and biting you--she likes to look at herself in the mirror, and will take any chance she can, which means you're dosing more often. The morning after the third day of use (and mind you, this is very disciplined use, with no re-dosing and very limited amounts ingested relative to the user's bodyweight), I found an unpleasant hangover (headache and mild nausea) and lack of motivation to do my normal exercising, etc. Urge to continue daily use was starting to develop, though quite mild, and would certainly build quickly if daily use continued (it didn't).
On a broader note, I think that dissociatives have a dark reputation in the psychedelic world for two main reasons. First, the high involves less of a temporal investment on the part of the user, thus opening up to more frequent redosing and more frequent use in general. Tolerance builds quickly and thus the absolute amount of substance being ingested increases quickly, such that the increase in neurotoxicity is marked. With acid or mushrooms this rarely occurs due to infrequent dosing and the fact that you're basically pissing out the acid already by the time you come down. This effect is exacerbated with the easy and continuous supply lines on which mxe is currently flowing, meaning that it's not like back in the day when your buddy finally scores a vial of ketamine and you use it like crazy for a month until it runs out, then it doesn't come around again for another few months or years.
Second, the reputation of dissociatives for producing intense and insightful out of body experiences tends to attract users who are not used to dealing with chemicals that have qualities that can easily lead to addiction. Thus, people who have no trouble keeping their use of phenethylamines and tryptamines under control need to understand that, yes, a dissociative can have many of the same emotional/spiritual/neurological benefits of a traditional psychedelic, but they need to be approached very differently. In a perfect world, people would only use dissociatives once a month or less, but that's not going to happen (myself included

). Very cliche'd but it bears repeating: you have your whole life to take more drugs, but once ingested you can never take less! I recommend drinking plenty of water before, during, and after using mxe or any drug.
Good nutrition and exercise habits will minimize negative effects associated with reasonable recreational drug use, and may even maximize their positive effects. Be careful, be safe, and we'll be able to continue using these mysterious and wonderful substances.