Anyone who tries to tell you that AJAX is a "new approach to web applications" is just rebranding old technology and hyping buzzwords, not engineering software in the real world. Because of browser and DHTML incompatibilities and limitiations, AJAX is like cocaine: it seems glamorous until you actually start using it, then the unintended consequences totally fuck you up.

Special Hazard Precautions for AJAX:

INGESTION: NAUSEA, VOMITING, AND DIARRHEA. EYES: EYE IRRITANT UPON DIRECT CONTACT. SKIN: MAY CAUSE SKIN IRRITATION UPON PROLONGED CONTACT. INHALATION: NONE UNDER NORMAL USE. PROLONGED INHALATION BY UNORTHODOX USE (NON-WETTED) OR ABUSE (SNIFFING) COULD PRODUCE LUNG DISEASE (SILICOSIS). N/K

Emergency/First Aid Proc: INGEST: IF EATEN/DRUNK--YOU MAY THROW UP. DRINK SIPS OF WATER/MILK. IF VOMIT CONTINUES, CALL POISON CTR/DR. EYES: IRRIT. FLUSH W/WATER 15 MIN. IF IRRIT PERSISTS, CALL POISON CTR/DR. SKIN: IRRIT. REMOVE WET CLOTHES. FLUSH W/WARM WATER 15 MIN. IF IRRIT PERSISTS, CALL DR/POISON CTR. INHAL: IF INHALED, MAY COUGH. TAKE SLOW DEEP BREATHS OF FRESH AIR, SIP WATER. IF COUGH PERSISTS, CALL DR/POISON CTR.

Here's the entire Ajax information sheet, with more warnings and hazard precautions.