Remember when the meme was "%90 of web apps will not reach a point where scaling is an issue"? Well, of those who do reach it, %90 will not reach a point when PHP's execution (assuming you use on of the existing code accelerator, all which are free IIRC and one will be bundled with PHP6) is the bottleneck.<p>It's a cool hack, but really targets Facebook-level needs. For most users, the downside (eg compatibility issues) will far outweigh the benefits.