I've now GMed three sessions in Roll20 and I thought I'd give a report. I make the maps in CC3 and use obsidian portal for the game wiki. Roll20 has become the most crucial element.
I've created "characters" for my monsters as I use them, complete with icons from pictures in a google image search. This makes it easy for me to improve fights as long as I've used the creature before. I put all their stats into them, which allows me to assign them easily to the three bars each token has. There's some nickle and dime tips in here I could pass on, but I won't bother unless someone asks.
The offshoot is every creature has a bar for hits, a bar that just has their AT/DB typed in, and another where I put bleeding and or penalties. I wish I had five, actually.
But because of this, I can run Rolemaster battles that would usually burn me out. Today, I had a village defense battle for second level characters fighting 18 goblins, 8 orcs and a Forest Troll in three waves. Previous campaigns, if I tried something like this in RM, I'd likely be burned out by the second or third wave, but I'm still stoked enough to write this post.
So while roll20 isn't crafted for RM, it really has really taken a lot of book keeping stuff off my shoulders.
I'll note that I DO use a house rule of one initiative roll for an entire combat. That helps a lot, but I could do it without that rule and I don't think it would annoy too much.