Let's look at what is probably the most popular chipset for the home builder today: the P35. We know it is suitable for mid-ranged users provided they don't plan on using integrated graphics because of the P, and that it has been around for a year because of the 3. The 5 means that this is the full implementation of the P3* chipset. So we know what Intel had in mind when they brought out the chipset, but an important note is that many manufacturers incorporated support for FSBs and memory times onto their higher end P35 boards that allow them to venture into the enthusiast territory Intel tries to reserve for its X type chipsets.
The 4 series steps up to PCI-E 2 support, but doesn't appear to have the performance or other advantages necessary to justify its price premiums over the 3 series, at least for now (see update below), with the former still being rather new. Furthermore, some combination of Intel making their chipsets more suitable for overclocking and manufacturer efforts have closed the gap on nVidia's chipsets' ease of overclocking. With many board makers' offerings based on the P35 including bios support to run a 1600 FSB CPU, this is indeed a very suitable chipset for a lot of users. Someone not demanding PCI-E 2 and planning to run a single GPU, or two Radeons and doesn't mind that one of the cards only gets x4 bandwidth, could definitely be very happy with this board.
Things are not as rosy for someone who wants to use integrated graphics and an Intel CPU, though. While the G boards share much with their P counterparts and are more than fine in that regard, AMD and nVidia's integrated graphics solutions for AMD CPUs are head and shoulders above what Intel has on its boards. While Intel is certainly improving its integrated graphics, the X4500HD on the G45 has an excellent complement of video connectors on the back panel and the ability to shoulder some of the HD video decoding burden off the CPU for instance, AMD and nVidia are putting actual GPUs farmed from their Radeon and GeForce cards right on the motherboard. Admittedly, they are dated, entry-level GPUs, but there is a big difference between even a mediocre graphics card and what is traditionally available in terms of integrated graphics. If you will be using the integrated graphics for anything more than Vista, you will at least want to consider what is happening on the AMD side.