[ Thanks to Michael for this link.
“For those that may have missed it, the ATI/AMD fglrx 8.42
display driver that was released last month had introduced AIGLX
support. The open-source ‘Radeon’ driver for ATI graphics cards
going up to the R400 generation has supported AIGLX for quite some
time, but the ATI binary display driver hadn’t until last month.
However, one of the complaints about the fglrx implementation of
AIGLX is that in the 8.42.3 driver, some are encountering slow
performance in Compiz / Compiz Fusion. We have taken an ATI Radeon
X800XL 256MB PCI-E graphics card, which is supported by both the
Radeon and fglrx drivers, and have compared their Compiz
performance in a few different scenarios…”