This socket is going to de disappeared in a few months. For a HTPC they are very good. They support strong enough processors for video encoding and capturing. [for more information click here]. Also these are low cost CPUs today and low power consuming.[unique for low nose htpcs] A Celeron 2.8Ghz costs about 90 euros and 3.06Ghz 115 euros. Although P4 478 seems to be already extinct. So if you are interested in a 478 solution hurry up!!!
  We could find only one 478 motherboard which is available in the market today.



Form factor: MicroATX 244mm x 203mm
CPU Socket: Socket 478
Supported processors: Intel Pentium 4(Prescott)/Celeron processor(Supports Hyper-Threading Technology)
Supported FSB: 800/533/400 MHz
Chipset:
- Northbridge: VIA P4M800
- Southbridge: VIA 8237R
Communication Ports: 1 x AGP8X/4X, 1.5V, 3 x PCI, 2 x SeialATA 1.5Gb/s, 2 x ATA 133/100/66 IDE, 1 x Floppy, keyboard PS2 , mouse PS2,6 x USB2.0 , 1 x parallel , 1 x LAN RJ45, 1 x Audio ( Line In/Out, Mic In),1 x COM port pin header
HDD support: Supports 4 AOA-66, ATA-100 and ATA-133 HDDs and 2 SATA hard disks
RAM sockets:2 x DDR DIMM DDR400/333 up to 2GB

Additional characteristics: embedded graphics card UniChromePro 3D Graphics(VIA P4M800 chipset supports mpeg4 encoding)
Embedded sound card with CMedia chipset CMI9761 and 6 channel AC'97 audio codec
Embedded LAN card VIA6103 10/100
BIOS:4Mb AMI BIOS with ACPI, SM BIOS 3.0,PnP