From the Ecstasy FAQ, available (with a whole bunch of really good drug info) at

Usual doses of MDMA range from around 80 to 160 milligrams (orally)...A benchmark standard dose is often considered to be 2 mg of MDMA per kilogram of body weight (though response to the drug is not strictly proportional to body weight).

When MDMA is taken by mouth, the effects manifest about 30-45 minutes later; snorting, smoking or injecting produces much quicker onset. The primary effects usually reach a plateau at T+1:00 (one hour after taking the dose) to T+1:30, stay there for some two hours, then start tapering gradually. The primary effects are pretty much over by T+4:00 to T+6:00. Secondary effects (afterglow) may be felt for days....

Supplemental dosing: If you have taken an ordinary dose of MDMA (say 2 mg/kg), you like where you are at about T+1:30 (you will have reached plateau by then), and would like to prolong your stay there, take a supplement equal to about 1/3 to 1/2 the initial dose. Taking much more than this is likely to induce or increase unwanted side effects without providing additional benefit in return.

The physical effects of usual doses of MDMA are subtle and variable: some users report dryness of mouth, jaw clenching, teeth grinding, nystagmus (eye wiggles), sweating, or nausea....

The psychological effects are a bit more difficult to describe, since they are many and of widely varying effects. The major ones are:

- Entactogenesis ("touching within"): This is a generalized feeling that all is right and good with the world.
- Empathogenesis: A feeling of emotional closeness to others (and to one's self) coupled with a breakdown of personal communication barriers.
- An enhancement of the senses: MDMA can significantly enhance (sometimes distort) the senses - touch, proprioception, vision, taste, smell.