In the aftermath of the TACA 737-300 dual engine failure in 1988 (emergency landing on a levee), a great deal of work was done regarding 'conventional' inclement weather threats to jet engines. Things like inward opening bleed doors (did a better job of scooping ice and water out of the flow path), and even subtle changes to the shape of the spinner would help direct ice and rain away from the inlet to the engine core have been implemented. Special 'icing tunnels' have been developed to simulate the threats and devise necessary improvement. As a result, the engines that have been introduced since then have demonstrated very good behavior in 'conventional' inclement weather.
At the same time, the rate of Ice Crystal Icing events has increased dramatically. There is plenty of debate as to why - global warming/climate change, more flights into the threat, or is there something about the newer generation of engines that makes them more susceptible (I suspect it's a combination of all three).
For a long time, most of the ICI events occurred in the South Pacific/Pacific Rim area, but that's been less the case the last 10 years, with a number of events occurring over the Americas.
Nemrytter, as I previously noted I'm not an expert, but when we did some Ice Crystal testing on a CF6 several years back, I believe they simply used large blocks of ice, with some sort of device that shaved off ice crystal material - the technique was heavily criticized at the time as not being representative, but no one had good suggestions as to how to make it better
Gaspath - The GE90-94B has indeed suffered compressor damage, but to date there have been no reported power loss or flameout events. Interestingly, there have been no reports of compressor damage on the GE90-115B, but I don't think anyone really understands what the difference is.
The PW2000 was in service for over 20 years before they had an event - then Northwest/Delta started basing a few 757s our of Narita, and sure enough within months they had an event (flameout at cruise) - in that South Pacific region which used to dominate the reports - and there have been a few more PW2000 events since then.
The GEnx events to date have all occurred at very high altitude - between 37k and 41k - and all at cruise. Very different from what we've seen on the CF6 that mainly have occurred during a descent at/near idle.
Nearly all the events have occurred either in the equatorial regions, or during the summer months in that hemisphere.
There have been a number of proposals to take a flying test bed type aircraft with heavily instrumented engines and go looking for ICI. Until recently those proposals have not gotten very far, but with the recent GEnx events that may change.