We haven't had any Linux compatibility troubles with any past Intel P35 + ICH9/ICH9R motherboards, and the ASRock 4Core1600P35-WiFi+ motherboard is no different. With Ubuntu 7.10 and other Linux distributions we had ran into no issues at all with everything from the ethernet to the disk controller to audio working "out of the box." In fact, the ASRock 802.11g WiFi adapter had even worked out of the box! The Realtek RTL8187L wireless ASIC is supported by Ubuntu 7.10 with the Linux 2.6.22 kernel and once powering up the system and turning to NetworkManager we had found our wireless networks. On the topic of hardware monitoring, with LM_Sensors 2.10 and using the w83627dhg-isa-0290 and coretemp-isa-0000 modules we were able to successfully read the system voltages, fan speeds, and temperatures. At this time Solaris/OpenSolaris is not compatible with the Intel P35 Chipset.
The testing hardware we had used with the 4Core1600P35-WiFi+ was 2GB of A-DATA Vitesta Extreme DDR2-800 memory, Western Digital 160GB SATA HDD, Intel Core 2 Duo E6400, SilverStone Zeus 750W, and an ASUS Radeon HD 3850 TOP 256MB graphics card. During benchmarking we were using Ubuntu 7.10 x86 with the ATI Catalyst 7.12 Linux driver. For comparison, we had also ran our select Linux benchmarks when the E6400 with the ASRock motherboard was running at 2.625GHz and had also re-tested the ASUS P5K-E (Intel P35) motherboard in the same hardware configuration. Benchmarks had included Quake 4, Enemy Territory: Quake Wars, LAME encoding, timed disk reads, Gzip compression, and RAMspeed.