Does serfdom and the Hagia Sophia stack?>? they both do %50 less time for workers to build improvements. And if they dont, does the Hagia just affect the workers in the city's zone or my entire country

Quick answer is yes.

Pretty sure both are global worker speed boosts. Strong in theory, but in practice much of your land will be improved by the time you get them, rendering them less helpful than alternatives more often than not. It's probably strong if you're spiritual, otherwise you have to weight the anarchy and other costs very carefully.

don't think I've ever built either, as I normally try to have enough workers for myself and another civilizations worker force by the time either become available. Could be extremely useful for clearing swaths of jungle though.

Don't forget that steam power gives you the same 50% bonus (though it obsoletes HS). These bonuses definitely do stack with Serfdom. However, I'm not exactly sure how they stack (does anyone know?) It's either:

(+50%) + (+50%) = (+100%) --> 2x worker speed, or

1.5 x 1.5 = 2.25x worker sped.

I suspect it is the former (2x) since that is how most multipliers in Civ4 work.

Having said that, many people on this forum don't seem to value worker speed too highly (they build/capture more workers) and don't often use serfdom or HS.

I am a fan of increased worker speed. It helps to play at epic or marathon speed, though, where it is more noticeable and powerful due to mathematical rounding issues. On normal or quick speed, the real delay in speed isn't working speed but movement speed.

If you have marble and the time to build it, give it a shot. More GPPs are always welcome in my book.

I am a fan of increased worker speed. It helps to play at epic or marathon speed, though, where it is more noticeable and powerful due to mathematical rounding issues.

I agree with this completely. If you play at a slower speed, halving worker build times is tremendously helpful. Especially on marathon, where it may take hundreds of turns to obsolete HS. If you're SPI, even better, as after serfdom stops being useful, you just switch over to another civic without anarchy. I might have to try this one day :D

I rarely build the Hagia Sofia for the worker benefits but for the Great Engineer Great Person points since there are so few ways to get GE points before factories/Ironworks are available.