I have been using USART for interfacing PICs to my PC for datalogging. The problem is that now serial ports are not very common and often you need a USB-Serial adapters which do not always work or have problems with drivers. I'm not a big fan of USB but I'm thinking of trying the USB-UART chip form Micrchip MCP2200-I/SO.
In your experience what is the most reliable and universal way of interfacing the PIC-embedded world to the PC/network enabled world!
The use of the USB to Serial Adapters work well if you use the latest drivers. I have had no problems what so ever when using the types of adapters based upon the chips from a company called FTDI. One reason that these adapters seem to work better is that the company directly supplies the drivers from their web site. They also put a lot of energy into maintaining their drivers and keeping them proven via the Microsoft WHQL certification process. The same cannot always be said for other small or "no-name" vendors and thus the reasons that unreliability and incompatibilities are seen from time to time.
An added benefit to the use of FTDI based devices is that the WHQL certification of their drivers gets them "in the box" with the Operating System. This means that on newer versions of Microsoft's OS that the serial adapters can truly be plug and play.
I personally have had good success with Silicon Labs CP2102-based USB-to-UART bridges. FTDI devices have been kind to me as well - I've taken some USB-to-RS232 devices, bypassed the RS232 driver IC and wired my dsPIC UART directly to the USB bridge IC with good success.
If you want bullet-proof compatibility (and your datalogging PC has a physical serial port) use a MAX232 or similar IC and convert the UART to RS232-compatible signals. The built-in RS232 ports on most PCs don't require drivers to work well.
If your PC doesn't have a physical serial port, you could use a USB-to-RS232 device and face the same sort of driver hurdles you may face with the USB-to-UART options.
