Great pack (I'm Tairgire's friend), it was just what I needed after getting burned out on all the five hundred tech packs that all claim to have a theme but then all add the exact same hundred or so mods. I was looking for something truer to vanilla, with an actual focus on mining and crafting, and RusticCraft aligns with what I wanted beautifully. I even enjoy that while my friend can focus on magic (Thaumcraft and Witchery), I can drill down through the technology that's available.
With regards to mining obsidian (at least until the fix is released), use steel. It looks like the Railcraft Blast Furnace is disabled, but in its place is the Steelworks High Furnace. Steel has a mining strength of manyullan. Pig iron is another alternative, but steel is easy to make and stronger.
Some things I've noticed:
If you're an explorer and can raid a few dungeons, food becomes a non-entity, even with Spice of Life. I have enough pizza, burgers, spaghetti, curry, hearty breakfasts, and beef wellington to last me another two weeks, even with diminishing returns (snack on some fruits and veggies from the plentiful gardens and the diminishing value of the bigger meals falls off quick). If you have a way to edit dungeon loot, I would probably reduce HarvestCraft food showing up by about half.
I can't seem to make the OpenBlocks Radio, but I've found about a dozen of the tuned crystal items as dungeon loot, making them pretty useless.
You can add waypoints to an Antique Atlas map, but I haven't found a way to delete them. I'm assuming I'm just too unfamiliar with that mod.
Deadly World is evil.
The Nether is evil.
You're evil.
I found a use for silver nuggets: 3 nuggets can be converted into 3 silver coins (Artifice). 1 silver coin can be converted down into 4 copper coins, which can be smelted into 4 copper nuggets. Or 4 silver coins can be converted up into a gold coin and smelted into a gold ingot. Just don't melt the silver because then you wind up with a tank full of molten silver and nothing to do with it.
I'm really enjoying this pack.