I have taken X with people before and not felt much. I had 250mg powder and snorted a line or two.
I felt very little and expect the powder was dirty - I've rolled on other pills fine.
The others around me seemed to be getting something from it. They went on to have more than me, but it seemed to working for them with the first 250mg, and I'm not trying to be tough saying I didn't feel it and I'm not completely burnt out - it just wasn't very good to me.
My girlfriend at the time said she couldn't feel it much either (it was our first time trying it). To an extent, it could be that you're expecting the wrong things from it.
X WILL NOT make you ultra happy or full of energy. That is the public image of it and it's wrong. If you're not in a happy and energetic mood before hand, it won't suddenly make it so.
I'm interested in the safety of drugs like X (beyond what the public are told) and went on a search for information. The drug is broken down in the bloodstream by a series of enzymes called the cytochrome p450's. Due to genetics some people have slightly more of these and some slightly less. The ones with significantly less may account for the tiny number of people who seem unable to cope with X. If you have slightly more, it could be that your body is breaking it down quite quickly so you don't feel as stimulated or for as long as others.
But I wouldn't just put it straight down to your body.
First of all, maybe the other people aren't used to taking heavier amounts and feel that a lighter experience is feeling the full effect - only you can judge that
Secondly, maybe you're expecting the wrong things from it - although, with a decent amount of X the effect should be in no way subtle. Again, not really immense and immediate euphoria, more an enhancing of your current mood, loss of anxiety, openness, focused but at the same time relaxed and calm, connected and a will to experience or learn. X won't immediately wipe out your personality, particularly at doses where you're still aware of what's going on. It can help modify it, but if you're holding on waiting for something to happen you can mask over the effect and just experience it from your normal point of view - making it easy to wonder if it's done anything.
MAOI's and SRI's won't wipe out the effect of X, they enhance it by causing even more serotonin to accumulate. You shouldn't mix the two because it can accumulate not just to a level that leaves you more depressed the next day, but into a kind of toxic shock level where you'll start experiencing the more negative effects like hypertension, sweating, shivering, nausea and all the like.
I've heard of people with depression taking X thinking it'll cure them. I feel reasonably sure in saying it won't - particularly if you go into experiences depressed. There's also a good chance you'll feel more depressed afterwards when it wears off (although, I've never really had a problem with crashing down myself). Neither can you continually chew through X whenever you feel a bit down. I don't believe it's anywhere near as dangerous as the public think, but it's not an everyday thing and dirty pills only make it more so.
I've written a few notes on this and was thinking of putting together a 'real world' guide to X based on things like this.
For example, a lot of other drugs (like cocaine, but also prescription drugs) are not only SRI modifiers but also inhibit the cytochrome p450 system, making it hard for your body to digest MDMA - which increases the chances of feeling the negative effects either during or after.
Be careful assuming you're getting clean molly. Too many people assume with powders and pills when things like coke are routinely cut to stupid amounts. Specially when molly is currently nowhere near as simple to make as it was ten years ago due to changes in the law - making it much more likely it's either cut or not actually molly.
BZP and TPMFF are new possibles for X pills I expect. RCs are still around but they're not so easy to score from the net now. The other two can be bought in bulk though and they do produce something quite similar to X, but not quite as deep and powerful - more superficial.
The X in Amsterdam is the reference for me so far. Tiny, pure, strong, almost a spiritual experience.