But, they handled it well and they've never screwed over their users and they have partially resolved the long-standing file transfer problem (https://xkcd.com/949/).
So I still have those concerns, but overall it's a great service and I've recommended it to a few folks over the years.
It helps also that there are some open alternatives on the scene now, so if you make Dropbox some critical part of your infrastructure, it's feasible to switch to something else if Dropbox suddenly decides they want to focus only on the smartphone market.
Slack had the ease-of-use and feature advantages -- which I acknowledged -- but it was too young and there were no open alternatives that matched it feature-for-feature. That made it dangerous to rely on too much. i.e., I'd still use it, but I wouldn't make it the de facto communication system for a company.
That's a strawman - no one said dropbox was useless to everyone: this is not about how simple it is to replicate the functionality, but who controls the data. The point gp was raising is that surrendering control your data to a 3rd party company has costs most people do not consider until it's too late - and this happens time and again ("oh no, this shit again"). How many stories have you read about downtime, account bans/freezes, and companies winding down or sold with little or no notice and no way to retrieve your data? Is it a worthy tradeoff for a shiny UI?