We've had a few tickets complaining about slow network speed, and not being able to access the full shared gigabit that we advertised.
100% of the time, they've been using the 100mbit realtek network adapter.
We've even had a customer cancel their VPS, with the reason being "False advertising, network is artificially capped to 100mbit". Turns out that their VPS was using the realtek adapter.
How many times have you gotten tickets about this, and how do you inform your customers to use the Intel or VirtIO adapters?