I noticed the same thing. I did a test with a file at ca. 700 MB recently, and cURLing via ipfs.io didn’t work the first time – sometimes also with smaller files, e.g. 100–250 MB: in my case cURL just timed out, in most cases after ca. 40 to 50 MB, independent of the original file size. But usually the second time around it’ll work. So at the moment, if you want to share a file on the IPFS, it’s good to cURL it at least once through a gateway, so it’s fully cached somewhere else than only on your own node.
As for the beta aspect, I haven’t run into any real problems, that I couldn’t pinpoint myself, and it was mostly due to file availability on the network, i.e. missing blocks etc. Otherwise it already seems rock solid, even the ipfs files API seems to be stable. The rest is development, for me primarily, what I’m looking for, is the auto-republication of ipns hashes that derive from different keys than “self”. Next big steps for me are file encryption, IP anonymity etc., but that’ll surely take time.