I had a noticeable increase in performance and overall stability when I replaced an inadequate PSU with an Antec TPII 550 on my personal system. And it definitely increased my OC'ing ability. It even reduced boot time. But nothing near a 30% boost in performance though.
Perhaps if your old PSU was a cheap bundled with the case PSU and your were sucking everything it had in it to power your system, it could seem like night and day with the new one. Kind of like walking out of a steam room and taking a deep breath of fresh cool air.
8 Pro 64bit
AMD FX 8350
Asus Sabertooth 990FX R2.0
24GB GSkill/Corsair 1866MHz
2x XFX 6870 1GB
SSD - OCZ V4 128GB/Kingston 120GB
HDD - 3TB/2x 750GB/500GB/250GB
Cooler Master HAF 932 Red
CM Hyper 212 EVO w/2x SickleFlow 120mm Red
Logitech X540 5.1 Surround
2X Acer 23" LED - Eyefinity: 3840x1080
Microsoft Sidewinder x4 KB
"The significant problems we face cannot be solved at the same level of thinking we were at when we created them."
- Albert Einstein