P.S. what's your start-up do?
The hiccups I've had have been DNS routing issues early on. It seems to have been solved, but for a while I was experiencing periodic enormous increases in latency (I think at one point the delay was 26 seconds). From what I heard they were specific to their linux VPSs (which is what I'm using), but those were solved around three or four months ago. I haven't had any issues since.
As far as the VPS goes, overall it's decent. I do a lot of my development over ssh so small latency blips are almost always immediately noticeable. Linode seems to still be more consistent, but just barely.
The biggest issue by far? Random VM Reboots
We thought our applications or some particular package was causing our VMs to randomly reboot. After thorough investigating, we found out that our code was perfectly fine. The folks on the Azure team were rebooting our VMs for internal upgrades. They oddly were doing this without any advance notice. This would affect our application servers, database servers, and even our development/staging instances. Another frustrating aspect was the fact that they would often do these upgrades during peak traffic hours (9 AM - 5 PM Pacific Time).
Without a better solution, we just wrote some code to ensure that our application supervisor would auto-start if the system were to reboot which helps mitigate the problem. Hopefully these issues no longer occur now that they offer an 99.95% SLA.
As for your other question, my start-up is Pepperdeck https://pepperdeck.com/
Just about every start-up I knew was using AWS or RackSpace. I was a bit concerned to go with them at first, but it was clear after investigating further that we wouldn't be locked-in. We're using Ubuntu VMs which are essentially identical to the ones we would have been using on AWS or RackSpace. Our app is fairly portable enough that we could switch if we had to do so.
There have been a few occasional hiccups, but we've been happy with them so far.