This is a tough one because the devices polled and data gathered is varied by device type (not just vendor). You're able to pull environmental stats from some, fan speeds, data transfer rates, CPU/Mem, etc, but not all devices support all of those polling features. It really depends on the MIBs used and if SolarWinds supports those MIBs - which they probably do. You'll really just have to do the leg work of adding in the devices (through auto discovery) and seeing what data is polled from them. You can dig deeper and add in additional pollers based upon specific MIBs if you so choose to get more granular with your stats, but ultimately you'll need to find that answer out by just using the software.
Usually out of the box for switches you'll get:
Interface Utilization Percentage
Environmentals if the device supports it
Not to mention, with UnDP (Universal Device Pollers) you can poll and report on pretty much anything that is available via SNMP. Just have to make your own custom pollers...
So I guess the answer would have to be - EVERYTHING!!