If I had 100 heavy armor and put +25 heavy armor for instance , would that be useless and not actually give any extra benefit at all?

While your armor rating would go up, fortify heavy armor isn't a very useful enchantment at higher levels due to the fact that, if you're making use of the perks that raise your armor rating (juggernaut, well-fitted, matching set), you will easily reach the armor cap if using daedric armor or something similar without the use of the enchantments.

There's an armor "cap"? I heard about guys who have armor that protect over 4000 or something, by using exploits... :confused:

567.

Gotta be kidding me right? I'm at 704 without having enchanted my gear yet lol

Nope, max phisical damage reduction is 80% and you hit it with 567 armor: http://www.uesp.net/wiki/Skyrim:Armor

Which means you shouldn't bother. You will take the same amount of damage with a 567 armor rating as you would at 10,000.

(Jaw hits floor) I guess that at least frees up opportunity for other enchants then

According to another thread its 672, sauce this thread: http://www.gamesas.com/index.php?/topic/1289727-2419-armor-6399-damage-using-smithing-alchemy-enchanting-only-33-perks-329k-backstabs-post-4/

personally i'd invest in magical resistances or health regen instead assuming you just want more defence.

100% fire and frost resist (which is quite easy depending on race and shop bought gear) laughs in the face of Dragons...and their priests...

Clarification for the armor cap: The game won't ever let your armor absorb more than 85% of incoming damage, which corresponds to an armor rating of 567. Which means that armor above that number is not useful.

For the initial question about skill bonuses above 100, yes, they can totally be useful depending on the skill. For example, The Heavy Armor skill increases the armor rating of the pieces you wear by 0.4% per skill point. Which means that at 100 skill, the Heavy Armor you wear is 40% better than it would be with 0 skill. If you fortify it further to 125, then your armor is 50% better. If you are still below the armor cap, this is obviously beneficial. If you are already above the armor cap, though, you would do better with another enchant.

Well this way you can wear almost every armor without gimping yourself; if you like steel armor the most, you can use it without problems.

He was just using heavy armor as an example.

What he was asking is if ANY gear or enchantment that boosts ANY skill still useful if that skill has reached 100.

Im not sure in Skyrim, but I think in Oblivion it didn't. And my stats were exploited like crazy.

I had permanent strength of about 1,100 (something) and blades at over 900, but my sword still did the same amount of damage.

Those dupe enchantment exploits were a real F bomb.

one thing i have read is that in terms of magic resists if you go beyond 100% it loops back round so 110% resist would only give 10%.

this is apparently a bug so you want to avoid doing that (also apparently its capped around 85% anyway)

this is quite easy to do as later on you can find 50% and 60% resist items on vendors quite often...

Ok, so lemme use the opportunity to clarify a question:

I have pickpocket 100, and i use the glitch of train a skill with a trainder and then pickpocket the gold i used back.

WIth pp 100 i had 12% chance to take 2200 back from a trainer, so i use a pickpocket potion to make my pickpocket 30% better for sometime, and when i go to the pickpocket that's 2200 gold, the chance become 0%.

So the question is: does the game really understand a skill that pass the 100 limit? Cos if pickpocket has this problem maybe other trees have the same problem too.

So the cap is no better then Oblivion's rating and they let us think it was more with higher numbers on our gear......LOL Because most people I think don't realize it is still 85% like OB.

Smithing definitely benefits over 100.

The way smithing works is that you can improve armour/weapons based on the skill level. Where it gets misleading is that putting a perk into that class of armour/weapon states 'allows you to improve it twice as much'.
What is actually meant is that the skill level required to improve to higher levels (fine, superior, flawless, epic and legendary) is less (but not actually as low as half, as implied by 'improved TWICE as much').
At level 100 you can improve any type of weapon/armour you have the perk for to legendary status. You can keep improving them beyond Legendary (still calls it legendary though) if you have more skill points (through enchantments I currently have 100 skill + around 80 in enchanted gear) so I can really improve stuff.

There is a table somewhere that shows skill requirements to improve to certain levels, the extra damage/protection that nets, both with and without the relevant perk.

Where people may get confused is that you CAN still improve to legendary and beyond, without the relevant perk, with a high enough skill level (168 is the first level of Legendary without perk from memory) so enchanting past 100 skill is very handy.

I imagine the same goes for alchemy and enchanting?