I havent had much chance to test them in PVP myself as I have only one character who I've been concentrating on, and I am still trying to stockpile the IOs before respec, ie none of the sets are slotted yet.
Personally Im with you, IOs in general offer slight improvement to the characters. I may revise my opinion once I get the sets to my blaster.
Most noticable difference on mine is the +hp combined with my accolades I have 400 more HP then a standard lvl 50 blaster 
Combine that with my improved regen and resistance shield makes him noticably more sturdy. Hard to tell how much difference other bonus' make as I'm usually heavily buffed.
thePhilosopher Martial Arts/Regen/Fire Scrapper
theRegulator Empathy/Energy/Soul Defender
Total Inertia Ice Blast/Kinetics/Psy Corruptor
Total Inferno Ice Blast/Thermal/Leviathan Corruptor
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I'm usually heavily buffed.
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Hacker, CHEAT, n00b!
As goes for IO's i can easily notice the difference on the toons i have done so far.
The word on the street is IO builds > HO builds. You only really use HOs as fillers.
Ive been slotting my lowbies mostly so far (lvl30-40), and I love them IOs.
My favorite IO combos are actually in PvE. Ive got my fire cages slotted with posterions blast: nrg dmg, and trap of the hunter: lethal dmg. Its fecking awesome.
A Paragon Defender
love IOs, use HOs in travel powers, IOs in everything else. on my empath i have +30% healing and +37.5% red rech. who can argue with that
my end problems have also been sorted on my tank and thermal i have 3 finished IO lvl 50 toons and i say IOs ftw!
I have to Say IO's HO's and Accolades for the best builds after playing about for a month and finish Knight Stalker. I personally still find HO's my first choice and fit in IOs around it.
I've been fighting IO'd Stalkers with my Kinetic the last two nights and it's been pretty even. They get me and I either escape or i got them with help from a team or my heavy lol. One stalker claimed he was at the stealth cap with stealth+hide+stealth IO. I wasn't too sure, but it didn't make much difference anyway as i was too quick for him. The only stalker that gave me trouble made good use of immobilise and -jump powers. Except i had Siphon Speed and can run almost as fast as Super Speed. Haven't really noticed if other villains had IOs slotted in PvP.
Right now I'm finding that focusing on IO's before level 30 isn't as effective as I want it to be...mostly because I just don't have the slots to double, triple, or quadruple stack the IO sets that work for me. My mind dom's focused on fear IO's (Glimpse of the Abyss is golden) for terrify/invokepanic/intimidate, and I'm finding my fear isn't being resisted at all the way it was before I had those sets almost fully slotted 3 times. Then again, I do have those powers slotted with ENHANCEMENTS so maybe that's doing a lot of the work.
As for the Teleport Stealth IO...I'm not finding that to have much effect...though I've yet to be jumped since I got it, so maybe that counts for something.
By the way...I need to go to Warburg and find out something about the Stealth IO. Basically I'm curious to see if the IO isn't active and then I teleport away from doom....do I reappear "stealth" and far enough away that they can't see me? I'm working off this assumption, but I just don't know.
-jared
After a month of I9 what does everyone think of IO builds in PvP? I think they are nice to have but not game breaking. I've only managed to get one toon nearly fully slotted and i notice the difference. When i've been defeated by regen rate means i don't have to use rest everytime i leave the Hero base in RV after being defeated.