I can say authoratively that the Conan system is awesome for more than just Hyboria/Howard. Besides using the system for Hyborian games (which is what I do most frequently), I've also run a game set in a low-magic, high fantasy world (Elves, Dwarves, giants, dragons, etc), and three quasi-historical and historical-fantasy settings (12th century Crusades, 2nd Century Rome, 15th century War of the Roses).
Generally, there isn't much that needs to be changed. Most things work as-written. All you have to do is drop the flavour text and change it for your own. The races, for instance, are simply a collection of stats. Change Cimmerian to Gaul or Aquilonian to German and the game still works perfectly.
Sorcery, in my games, has always stayed and is relegated to the same role it serves in most of my Conan games -- where very few people are actually spellcasting scholars, and even fewer are PCs.
The biggest changes for me have always been in the equipment section. My Crusades and Roman games required a lot of tweaking to the available weapons and armour to fit the period. Even so, I didn't have to do much of anything to make it work, besides drop a few items that shouldn't be available (like plate armour and such).
If you're running a homebrew setting where the equipment section wouldn't need any changes, you'll likely find that almost nothing, rule-wise, needs to be changed, unless you have vastly different ideas on how spellcraft should work in your setting. I like the way it works in Conan, and that's how I use it in homebrew settings, so that's never been an issue for me.
