If you're starting Mass Effect 3's new Citadel DLC, you'll have to follow a few steps to get going. It's a two-part download, the first part is the one you pay for, but you'll have to manually search for the second part. (I found it on the XBLA page with minimal hassle.)
We only ever hear negative things about customer service, because a satisfied customer rarely spends time gushing over their experience on the internet. Commenter KillerIri5h is an exception, raving about his Xbox Live customer service experience in today's Speak Up on Kotaku.
Within a minute of logging into my trial account at games-on-demand service The Happy Cloud I was playing the full PC version of LEGO Batman. "Instant gratification" is a phrase the company likes to toss about, and it certainly fits the bill.