Their complaint is that Calc sometimes lags/hangs with a few thousand rows of heavily formatted data (they're not a data scientist, but still need to deal with government-issued xls[x] files). It wasn't a serious problem though and a great opportunity to "look under the hood" of what was happening and introduce them to CSV files. The other "problem" is that online shopping websites are often horribly slow, but again, I'd say there's a lesson in there and it could be viewed as a feature.
So all in all I am a huge fan. I think it's a great way to onboard people on good-enough-computing and open source. There is something magical about its form factor that resonates with "non-technical" people. Also quite cheap and accessible.