FTP (or much more secure FTPS) gives best performance for network file transfer (it's in the name!).

If you're looking for (file transfer) performance, it's better to choose esata enclosures, which aren't more expensive (esata is sata!), just more difficult to find. However, with esata you will need external power supply. If you like DIY, you can externalize the plugcomputer's PSU to also feed the drives (but check the maximum power for the PSU).
To stream 720p video (I assume H.264 encoded), about 5Mb/s is necessary, so anything (usb drive, 100Mb/s ethernet) will do.
The guruplugs appear to have heating problems, so I would suggest getting either an esata sheevaplug (I have one ordered from NewIT, it rocks, never had a problem) or wait a bit for the dreamplug if you want more connectivity.
PS: some say NFS is faster than Samba.

about the (presumably) NAND problem, you could (if you get the dreamplug back soon) edit /usr/src/linux/arch/arm/mach-kirkwood/sheevaplug-setup.c and comment the line kirkwood_nand_init(ARRAY_AND_SIZE(sheevaplug_nand_parts), 25);
(the good way would be to add an if statement before to differentiate the models with arcnumbers, like for sheeva/esatasheeva).

Is there any chance you could run a test on the usage of both gig ports at the same time?
Something like sending /dev/zero on one device to /dev/null on another device, via netcat? And do it twice (to use both ports), in order to confirm that there are no more heating issues?
Thank you very much

Or maybe you mounted it read-only.
Could you give the results of 'mount' and 'ls -ld /media/500gb'?
Also samba should write some stuff in a log file, look in all relevant logs in /var/log.

Martin, there is an u-boot somewhere that supports esata (i boot from esata), but I can't remember which one.
I'm pretty sure I found it on this forum or the newit forum.
I oculd give you a checksum if you want, or give you the binary.

I forgot to mention I use an esata sheevaplug (with esata). You may not be able to reach this speed via usb or sd card.

I use pure-ftpd, it works perfectly, and it is quite easy to configure.
Transfer rate is about 45/50MB/s when connected directly to another computer via (gigabit) ethernet.
What is the link between the computer and the sheevaplug, when you're experiencing problems?
Also, what's your current ftp server?

very nice.
can it flash uboot if the plug is bricked (bad uboot)?
thanks

It's actually a SMTP server that you want (server to which you can send mails), and then maybe a pop3/imap server (to read/retrieve mails from elsewhere).
Look at qmail or postfix (maybe there are other, smaller programs).
You will also need to set up your DNS accordingly.
To sum up, there is no really quick way, as there are at least two (three with pop3/imap) servers involved (you could also want webmail for example).
So you need to read some doc, sorry!
PS: I've read somewhere that the gentoo doc about qmail is good (replace emerge with apt-get, config should be the same), maybe you should start there.

or you can boot the gentoo install from tftp (search gentoo sheevaplug on google, this gives you an initrd and uimage), and then edit the passwd file.

initrd is not needed, actually your bootcmd_sheeva_sd doesn't use it (and if it succeeds, bootcmd_debian_sd is never run).
So are you booting the sheeva-uImage now?

same here: http://plugcomputer.org/plugforum/index.php?topic=1408.msg8678#msg8678, definitely seems to be uboot-related... I'm confused

I compiled a vanilla 2.6.33 + sata patch (the one modifying sheevaplug-setup.c), and with the original uboot (I have an esata sheeva from newit), which is marvell version 3.4.16 I think, it hangs when initializing sata_mv:
....
Serial: 8250/16550 driver, 2 ports, IRQ sharing disabled
serial8250.0: ttyS0 at MMIO 0xf1012000 (irq = 33) is a 16550A
console [ttyS0] enabled
loop: module loaded
sata_mv sata_mv.0: version 1.28

and it hangs at that point

using the uboot found here: http://www.naobsd.org/sheeva/ (I had to flash uboot to load the kernel from a sata HD whatsoever), no problem.
So apparently uboot changes something... this is quite a mystery to me  
If anyone has an explanation, I would be very interested.
Btw, is there an "official" version/repo of u-boot? It seems everyone patches an already patched version etc. What is recommended?

I tried some cross-compiling with portage, and in general it works great, it's amazing!
However, some packages are (according to what I found on google) impossible to cross-compile (libperl and perl, for example), due to custom config scripts (I realized the autotools are nice after all). Too bad!
I finally ordered an esata plug! I think I'll try with distcc first, as you suggested. I'll see later for more custom installs.
The kernel is built, I'm gonna install a stage3 on a usb stick tonight, but it's hard to wait for the actual plug