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A link, to a link, to failure. If Google can screw it up with 5 tips, imagine 10x more failure with pretty pointless 'tips'.

Index you database, cache your byte-code and the output. Don't bother with the micro-optimisations.

I don't understand why (if there are no side effects) ++$i is faster than $i++; the 'compiler' should view both forms as ++$i.

Isn't "PHP optimisation" an oxymoron?

Micro-tuning is fun, but not terribly useful in most cases. In most web applications, the performance bottleneck is in interacting with external services - typically a database. Performing all of these optimizations will typically net you less time than the standard deviation of a single database call - meaning the performance improvements simply get lost in the noise.

There are lots of ways to get your web app to perform better. Micro optimizations that net you a few microseconds here and there should be pretty far down on the list.

True optimization tip for php is "Don't do stupid things".

You got three or more levels of nesting in your loops?
Do you pull a lot of data from sql to calculate some summary with php that could be done in sql instead?
Do you use loop if the function exists that will do the same with single call?
Do you include lots of files and not use APC cache (or equivalent)?
Do you use files to store your data?
Do you process more than few hundred kB of data in single script?
Don't you use cache to speed up long operations that calculate rarely changing values?
Do you eval often ?