Running the following two commands in-game consistently causes the game to crash (error #132).
/run for itemId = 20000, 23000 do GetItemInfoInstant(itemId) end
Doing 2k requests does not cause a crash. I couldn't find the exact threshold since it didn't appear to be constant, even with no addons enabled. Doing it as 3 separate requests (1k items each) still results in a crash.
My addons do use this API quite a bit, as it seems to be the best way to get the information it provides, rather than calling GetItemInfo(). Having the game crash every time I reload my UI is quite annoying :P.
I'm guessing GetItemInfoInstant() is caching results somewhere, and calling it so many times in a given session is corrupting the cache somehow, leading to a crash when the UI loads next.
FWIW, I believe this started happening with 220.127.116.1110 as the first time it crash log I have is 10/14, and I generally just open WoW on the weekends.