I have had both forged and cast lowers.
There were some cast Olys that had problems, but it was due to machining, holes not being located properly. That problem was resolved.
Yes, forged are stronger, but so? I have seen a few reportings of cracks, but those would be promptly replaced by the mfg, I am sure.
I have owned an Essential Arms cast lower, and its fit and function was perfect. No issues. I have since seen many others, and never have I seen a malfuction issue associated with the fact the lower was cast vs forged. In fact, no issues at all with the Essential Arms lowers other than some did not like the gray color.
Johnnytac mentions the SOCOM milled, but then cautions about some early out of spec units. Should that fact be used to trash all SOCOM's? I don't think so.
Yes, forged are stronger. Is that extra strength necessary? I am not so sure. A primary defense rifle? I would probably chose a forged receiver. If I was offered a good buy on a complete rifle or just a lower? I would not immediately turn it down based only on the cast vs forged construction.