What kinds of surfaces do I use it on? What surfaces should I avoid? Should I use a cleaner with it like Mr. Clean or Windex?
What does the package say?
I’ve used mine on plastic, fiberglass, painted metal, glass, vinyl, painted wood and walls, tile… And mostly, I’ve just used it wet, without any soap, or with a little bit of dish detergent. YMMV
They work well on the white plastic handles on my fridge & freezer doors.
They’re amazing on the non-slip bumpy surfaces on our boat.
I looked at the package and apparently it’s not for sinks or tiled countertops. I’ll try it out on white fiberboard doors and baseboards. Can I use it on stainless steel?
They’re great for removing that caked-on oil residue that builds up on your range hood or backsplash.
Don’t put any soap on it or use spray! Get it wet and squeeze it mostly dry then go to town.
Don’t use it on matte or satin painted surfaces but it’s great on glossy paint surfaces.
I like to use it on my kitchen walls where there’s some grease/condensation buildup. And on the other white glossy walls where the dogs and I got mud from our feet.
Baseboards and especially bathroom baseboards are good spots.
All of your light switch covers. And the walls around them.
Erase Mr. Clean! 
White bathroom fixtures. Stainless anything. Microwave in and out. I have granite counters so I don’t use them there. (Note to self: ask ~VOW about my countertops)
Refridge shelves, glass and plastic.
I don’t like them on windows.
Aluminum wheels on cars.
I’ve had the opposite results. I’m leery to use it on anything with a shiny finish as it seems to take the finish off and dulls it. Used one on one of those plastic shower inserts and noticed when I was done that the plastic now had a matte finish and got dirtier faster.
I have shiny laminate flooring that I don’t dare use it on as I’m afraid to take the finish off. It is a micro abrasive so I’m pretty careful with it.
ETA- a quick google search warns not to use them on granite or marble countertops, stainless steels, wood, or glossy surfaces
It’s basically really, really fine sandpaper, so you wouldn’t use it with anything you don’t want to abrade.
If you really like it but don’t want to pay a premium, look up “melamine foam” on Amazon and other places.
I haven’t use the Eraser on tiled or granite countertops. I do use it on damn near everything else.
I’ve used just the Eraser, dampened, and I’ve used it with Comet or spray cleaners. No Eraser Police came to my door and busted me for Eraser misuse!
I try not to use it on textured surfaces or nonstick surfaces, because the Eraser tears and crumbles. While I wish I could use it on EVERYTHING, it’s simply a miracle product and I love-love-love the results I get on everything else!
Do not use it on any eating or drinking utensils. I do occasionally break that rule by cleaning the animals’ various water dishes. Those things get so gooped up with crud! BUT! After using the Eraser, I thoroughly wash the dishes with soap and water.
Years ago, pet food was found to be contaminated with melamine, and some animals died. The Eraser is made out of Melamine, and I don’t want any melamine residue to contaminate the water dishes.
Wouldn’t a Mister Clean Magic Eraser toothbrush be something else?
~VOW
Hmmm? You give me ideas. Imma try one on Mr.Wrekkers bridgework. They’re in a cup on my sink right now. I report back with results.
Don’t worry I’ll use a new one. And I’ll rinse the bridge after. 
Since it is stronger. I use that to clean our oven toaster and oven.
I’ve dampened it and gone around the downstairs cleaning scuffs and marks off of the baseboards, doors, and doorjambs. It works like a dream! Annoyingly, I’ve discovered that what I thought were a few scuffs were actually gouges in the wood. After the sun comes up and I have better light I’ll examine the white-painted metal parts of the sliding glass door and remove any crud.
Even though sinks were not pictured on the box as what you could clean, I experimentally took a swipe at some aluminum pot marks in my white porcelain sink. It removed the marks in one or two rubs! I usually have to use a scrubby pad, some Comet and elbow grease.
A door in my bathroom gets a tacky accumulation of hairspray mixed with normal house dust, and it usually takes rubbing alcohol and scrubbing to clean it. I’ll try the Eraser on it later today and see what happens.
A new convert!
~VOW
I use one to get the grass stains off my sneakers after I mow the lawn. Second on using it on the range hood! They’re also good for getting the gunk off the stove knobs and removing kitty footyprints from my window ledges.
I’ve recently been loading the archived contents from lots of 10+ year-old DVD-Rs on to an HD. Some of them have unreadable files because of scuffing. Would one of these be a viable buffing option?