I'm sure most of you have seen but I had Weapon R intake installed on my car recently:
New Weapon R SRI Installed
I'm a skeptic on intakes, but it does sound better. They said on dyno it increased something like 3-12 HP depending on range. Wish I saw dyno graph but didn't.
As for the AEM vs. Injen debate/flamewar going on, they're all filters-on-a-stick, so it's not like one brand is going to be dramatically different--provided they get the MAF stuff right. Both use gauze filters, similar diameter piping, etc.
They key factors for good intake performance are the following:
1) Piping curvature: Are there sharp angles that will reduce the air flow into the intake manifold?
2) Location: Are they placed in an area in the engine bay where there's good air flow? This is the main strength of a CAI over a SRI.
3) Filter: Does the filter provide good protection as well as good air flow? Oiled foam filters such as my Weapon R provide better air flow--but some have questioned its long term durability.
4) Heat shielding: Does the intake absorb a lot of heat from the engine bay? In spite of the touted benefits of CAI, I think the chief strength of them as opposed to the SRI is that they don't have the heat bog that cause sluggish launches. Once the car's moving at 40mph, the engine bay doesn't have enough time to really heat the air.
Unless people have done comparisons with the diff brands, it's all hearsay and preference at this point. "No no Injen is teh best!!" comments don't have much backing if they're not based on dynos or from using multiple intakes.