Thanks for all the helpful replies!
Some comments:
* Yes, I meant to replace healing surges with fatigue points. I'll clarify that in the original post.
* As I explained in the original post, the reason for the name change (and that numbers go up rather than down) is purely aesthetic: it avoids having "negative healing surges".
* I'm not going to respond to the nitpicking replies regarding time. Why bicker about whether the time spent adventuring totals 10 or 30 minutes? That won't change the fact that any party will commonly spend 23 hours out of the day resting.
Just like in 3rd edition!
I disagree with your assessment of the problem; I have found my pcs running for three sessions, including hours of exploration, multiple trap-monster combos, etc. without taking an extended rest.
How many combats have they had?
My experience is mainly in playing Keep of the Shadowfell with a 4-PC party. On average, I'd say we have needed two extended rests per session.
This might change with a less combat-intensive adventure (KotS is a pure dungeon slash).
Edit: But to be more helpful, I'd say that your proposed system is a good start, but what if the pcs just keep going? Is there a point at which the penalties get worse? I would recommend it, but I'm not sure how you'd want it to work.
I think so too. I didn't include anything like that, because I wanted to start with basics. Remember, the purpose of the rule is to let the party move on even when one PC is at low or zero healing surges (=near or at his fatigue threshold), assuming the rest of the party are fine.
When everybody (or almost everybody) is low on resources, resting is much more natural and much less of a problem. Being able to press on in this case isn't the intention of the rules, so yes, some additional discouragement is probably a good idea.
Here's a solution: Quit running all-standard encounters. I've noticed too that one or two characters tend to run out of healing surges after 3 or 4 standard encounters. Then I started throwing in some lower-level fights in between and BAM, upwards of a dozen encounters before they need an extended rest.
I understand your point, and probably this is what we have encountered in KotS.
Not sure I like the remedy, though. If the system requires you to have easy encounters for the resources to last through-out the session, that still seems flawed somehow. Sooner or later, the lack of variety ("always easy encounters") is bound to get boring. I'd much prefer a solution that's robust enough to handle the full variety of encounter strengths the system can throw atya.