Skill checks and attribute checks are pretty common. Often "roll d20 under your attribute" is the standard default. Maybe there are modifiers. Maybe there are difficulty levels.
Some other bloggers are doing some interesting work on this too. Check here and here. They have great ideas. I put in my $0.02 here as well.
Here's a simpler update. I want to have both modifiers AND difficulty levels AND I want to keep things relatively simple. Some kind of "target number" that can be noted down at character creation and used throughout play.
Here's my proposal. It hasn't been tested in play -- YET -- but I have a Megadungeon campaign running, so it won't be long. If you try it out; let me know what you think. I think the system has great potential.
Target number (or less) on d8
Modifiers to Target Number (may apply to one or both dice – DM's option)
In your “idiom”
+1 for every fraction of 5 levels
(V) Very Difficult
A roll of 1 will always succeed (otherwise why are you rolling?) A roll of 8 (the Ocho) always fails.
Single Attribute Challenge: roll 1d8 and see if you roll less than or equal to your target number. If you do – you succeed. If you don't – you fail. No big deal. If you roll an 8; roll again. On another 8 – something of a notable calamity has occurred (fun, but not necessarily deadly).
Dual Attribute Challenge: roll 2d8 (color coded for each attribute). Must roll equal to or less than your target number for each die. Thus, if a character was climbing a slippery, steep incline (STR and DEX) and their STR was 13 (Target 4) and their DEX was 11 (Target 3) If one die fails – the character fails. This may suggest the nature of the failure and the consequences. If you roll double-eight (Crazy Eights), something calamitous has happened beyond mere failure (should be interesting, but not necessarily deadly).