According to a report from research firm In-Stat PCI Express has been quickly adopted, with "virtually all" PCs and x86 servers now integrating the technology.
This may be true for new PCs that are shipping right now but there's still a huge amount of old AGP systems. The best proof for this is that graphics card makers are still launching mid-range and even some fairly high-end graphics cards with an AGP interface.
The market research firm estimates that PCI Express was used in 17 million boards in 2006 and will make its way into 37.2 million boards by 2010. By then, a total of 440.2 million devices will have shipped with PCI Express, In-Stat believes.