I bought a Foxconn
P4M9007MB-8RS2H over a month ago but haven't done anything with it. Still in the box.
According to Gary Key's quick summary of extensive tests performed for his unfinished review of numerous mATX boards and chipsets, boards using VIA's K8M890 put in a solid showing and would have been the 'overall leader' in price-to-performance ratio had the integrated VIA Chrome9 graphics been stronger against the NVIDIA and AMD offerings. The P4M900 is essentially the Intel version of the K8M890, both use the Chrome9 IGP and VT8237A Southbridge.
However, the P4M900 has a weakness that K8M890 doesn't - no dual channel memory support. P4M900 can only do single channel memory. This will probably bring the numbers down a bit for P4M900 since its competitors support dual channel. As to how much, all comparisons with previous generation P4 showed that single channel wasn't exactly a deal breaker.
Even while many were insisting that high-end Northwood and Prescott models with 800MHz FSB would be "crippled" by single channel, numerous tests using non-synthetic benchmarks showed that the performance of single-channel chipsets like Intel 848P and VIA PT800 lagged not more than 10% behind the fastest dual channel 865PE and 875P enthusiast motherboards on the market (most benchmarks were around 5%). Had they tested using 'average' 865PE and 875P motherboards instead of the top-performing enthusiast boards available, the difference would have been negligible.
Dual-core Intel CPUs probably benefit more from dual channel bandwidth than previous generation P4s, but I doubt that "crippled" would be any more a fitting characterization. I would be surprised if the difference exceeded 15% in most real-world things compared with competing dual channel IGP boards in the same class using a PCI Express graphics card instead of the onboard stuff. Using the integrated graphics definitely will result in a greater performance hit than single channel. Even a cheap PCI-E card like a GF6200 would perform significantly better than the IGP.
P4M900 supports up to DDR2-667, so you might as well go with at least DDR2-667 since it costs the same as DDR2-533. DDR2-800 would be the better choice if you plan to get a better motherboard in the not-so-distant future. You can get 1GB of DDR2-800 for about $50.00 shipped.