Toras said:
I will be the first to admit that 3.5 DR rules are interesting, and not at all unappropriate.
The problem I have with it is that it makes Power Attack a required feat, and puts the shaft to any duelist or single one handed weapon fighter. Any 2-handed fighter can get through DR like it was nothing, any archer has an arrow or two for any occasion, and the 2 weapon fighter will likely have at least 1 weapon that might be effective.
First off, after a full year of using 3.5 DR in my campaigns, I've *NEVER* seen the golfbag syndrome. What I have seen is that party's tend to acquire an occasional cold iron, alchemical silver or adamantine weapon over time. Most players don't make a big deal out of the weapon's material type. Given a choice between a +1 cold iron sword or a +1 flaming sword, most will take the flaming sword. Still, most players won't turn down a weapon made of a special material and will tend to hang onto it as a backup weapon. Rarely does the party have more than 1 or 2 weapons of any given special material - a silvered dagger here, a cold iron battleaxe there. No golfbag... just a nice feature you sometimes opt for.
The DR rules do make Power Attack a viable and popular strategy for overwhelming DR (hell, Power Attack is almost a must for any tank even if we ignore DR entirely). Sneak attack damage dice can also help overwhelm DR (at least against critter vulnerable to such damage). A nice big + on a weapon along with other damage bonuses (e.g. strength, weapon specialization) can overwhelm DR. Bane weapons are great for overwhelming DR. Finesse fighters often have sneak attack damage (when flanking) or other sources of damage enhancement. Spellcasters can, via several spells, temporarily allow a weapon to bypass DR.
In any case, DR5/whatever tends to not be a big deal if players lack the bypassing attack type. If the party lacks the means to bypass DR5, it just means the creature is tougher. Lots of these weaker DRs offer either a common attack type (e.g. bludgeon) or multiple attack types (e.g. cold iron or good) to bypass them.
DR10/whatever is worthy of respect and will make a critter a whole lot tougher if you can't get around it. Most frontline PCs of appropriate CR will tend to be able to produce over 10 points of damage on attacks, so they can still overwhelm it. Still, having to overwhelm such a DR means nickle-and-diming the creature to death or relying upon your spellcasters to inflict the bulk of the damage.
DR15/whatever or more is a very serious foe. Few unexpected encounters (except perhaps at very high level) are of this caliber. Odds are you know that this creature will be your foe or you are so powerful that you have the means to get around its DR.
This is doubly true for any creature with a high DR that requires X and Y. A smart party should be seeking out special weapons to defeat such a beast if they don't already have them. If you plan on facing a pit fiend, then maybe it's worth going on a side quest to find the Holy Silver Sword of St. Philbert first.
High DRs that a party can't overcome will make frontal assaults ineffective, true, but I've seen those situations bring out some excellent creativity in players. The rogue who's rapier isn't hurting the construct starts tossing alchemical grenade weapons, or using the aid another action to assist the power attacking barbarian, or luring the creature away from the spellcasters (or into a booby trap).
. It often was also a good explaination why it had to be the characters going against the monster - nobody else had a chance of hurting it. 
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