This laptop works very well under Linux and the 12.1" TFT screen will do 1024x768 making it a joy to use despite its age.

The speed with Debian 3.0 using icewm as the window manager (with dfm providing desktop icons) is very acceptable although huge apps like OpenOffice or Mozilla would try anyone's patience.

Graphics
The graphics chipset is a Chips & Technologies ct65550, I've got it running in 1024x768 at 16bpp with the following mode line:
ModeLine "1024x768" 53 1024 1032 1176 1344 768 771 777 806

Sound
The sound is provided by the Crystal Semiconductor CS4232 chipset and works fine using the standard cs4232 module with the following settings: io=0x534 irq=5 dma=1 dma2=0 mpuio=0x330 mpuirq=5

Mouse
The built in Accupoint mouse is a PS/2 type on /dev/psaux. I love the Accupoint style controllers, definitely my favourite method of laptop mouse control.

APM (Power Management)
Both standby (apm -S) and suspend (apm -s) work. No special configuration or partitions are necessary for suspend as the suspend mode on these machines is done purely in hardware. When the laptop is put in suspend mode, a backup battery provides enough power to keep the memory refreshed. The normal "working" battery is not used and can be removed. The backup battery offers anywhere from 8-12 hours of power.
The resume seems to fail if the pcmcia cards aren't ejected (cardctl eject) before suspend although they will be automatically reactivated on resume.

Modem
The 720CDT has a built in 28.8 hardware modem which works fine under Linux. I use wvdial on this machine but that is just a personal choice and is not necessary.

BIOS
Toshiba provides an executable for Windows machines for entering the BIOS, however you can also get into the BIOS by pressing the Escape key while powering on. Once you get the message, press F1 to enter the BIOS.

Other - PCMCIA & IrDA
Worked out of the box with my D-Link DWL-650 Wireless NIC but note the small problem mentioned above regarding resume. Doing a 'cardctl eject' before suspend works round this nicely.

IrDA
I have not had reason to try IrDA yet.

Links
The Toshiba Linux Utilities: Suite of applications for using Toshiba laptops with Linux, includes TuxTime (similar to MaxTime for Windows - allows the user to set things such as LCD backlight settings, hard disk auto off times, speaker volume etc) and Fan (for controlling the internal fan).

Full Specifications from Toshiba in PDF format.

Linux On Laptops page on 720CDT - note the bit about the modem being a winmodem is not correct.