The European Commission just published an interesting document on the long-term career development of Marie Curie researchers: Marie Curie researchers and their long-term career
development: A comparative study". You can find it here (executive summary).
in general, it seems that Marie Curie programs have a positive effects on multiple indicators of career quality (although not speed). This part was particularly interesting:
"No particular effects on career ‘speed’ were registered. MC fellows achieve professorship titles more frequently than other fellows, but this seemingly requires more time than for researchers with smaller mobility experience, i.e. those that tend to stay in the same institution throughout their entire career. Here, an ‘affiliation effect’ can be observed which rewards non-mobile researchers within certain academic environments and penalises somewhat mobile ones."
This is very likely to be ascribed to the typical recruitment of European Universities (Spain and Italy for example), in which the "internal" researchers is heavily supported by the local hiring committee. Thus, staying in the same place for (almost) all the career may be a wise decision. Sad thing.