I can't answer about the continued cause of download errors (I don't think it was ever pinned down in these fora), but for me trying-trying-trying-and-trying-again let me install pretty much everything I wanted to.

(This was without the "repostory" fix. I think I noticed an improvement in my download success rate after removing the "i", but I can't say for sure.)

Some apps took one try, some took five, some took more like fifteen. I'm not sure what's going on here (busy servers?), but for those of you who aren't finding an answer and are dying to install a certain app, keep on trying! Good luck.