Thank you, David. You're quite right to caution me against throwing out the proverbial baby with the bathwater in this instance. I completely concur that the desktop version is an amazing product, it would be rash to swear off using it based on this experience alone. But given that I had already had some (albeit relatively limited) experience with the desktop version, I already knew that Wolfram were capable of producing exceedingly high-quality products, I think that I was more frustrated by the apparent lack of customer support on their part. They did, however, eventually get in contact with me, so it turns out that I was just being a tad impatient.

I think your feedback is very valuable, and I know that Wolfram employees read this page in detail. I would hope that they contact you to learn more in detail about the nature of your Mathematica Online experience and then move that information into the iterative development process for the product. I'd think that they want it to be as responsive and usable as possible based on the underlying technologies. But, given that, I would recommend that (in the heat of the emotional moment of being angry at the experience that you are having--and rightly so in many ways), you do not "throw the baby out with the bathwater". Desktop Mathematica is an amazing product and incredibly useful. But clearly there are (keeping with the baby metaphor) birthing traumas for aspects of the Online version.