I've used Roll20 for a couple years on and off now. Right now, we are playing FFG's Star Wars with it, but only use it as a place for us to roll the die so everyone can see it.
My internet connection is terrible (I recently clocked in a record low of 68 Bytes/second) so Roll20 has been a mixed experience for me. That said, even with my






internet, it has been a mostly reliable place to play games with friends in different countries.
My biggest complaint for Roll20 is that it does not give you enough space for everything. If you want to look at the map on the screen, run the initiative tracker, and open a note which has enemy information on it, you're pretty much pushing the limits of screen real estate. The files, character sheets, and notes tabs can get congested over time. When I ran a long campaign in DnD on Roll20, I had to put folders into folders into folders to keep everything organized, and checking which was available to be seen by which player was a bit tiresome.
All that said, I've never lost any data and never heard of anyone losing data. Character sheets stay on there indefinitely and aren't at risk for being lost. When we switched systems, we moved gamerooms and whenever we want, we can return to the first gameroom and continue right where we left off. The grid and map are reliable and simple to interface with. Players can do almost everything the GM can do if you want them to.
The tokens and other resources for free leave a lot to be desired. My players ended up drawing their own pogs with Roll20's drawing tool. We then moved them through crudely drawn dungeons whenever it came up. I do more theatre of the mind stuff, so it never became a major problem.
The Roll20 wiki and forums will have plenty of guides to making macros.
The Roll20 Wiki and the forums have pretty much every question you could come up with. They're an excellent resource for sure.