After deeper review I found that unfortunately SyncBack not only depends on the registry, but the whole profile system is rather clumbsy (IMO). It can be made to work OK but I'm going to take a second look @ Unison (I was bothered by some of its apparent complexity while the simplicity of FTP had appeal...).http://www.2brightsparks.com/downloads.html#freeware
This is yet another file synchronization util that also works with FTP sites.
I'll still use SyncBack for personal use, but it's not going to meet my school's criteria for portability since it introduces problems w/ it's profile mgm't.
As for the %varname% "hack", I recommend it highly for other portable uses where relative paths pose a problem with recalcitrant software.
After reading more about the use of rsync, my caution about NSTI conformance seems even more prudent...SyncBack is not 100% compatible w/ portable environments however, because its profiles want a complete path ( <drive letter>:\dir\dir\dir\ ) and it won't take a relative root like "\apps\blah." However it will take environment variable substitutions using %VARNAME%.
With that realization I found a work-around that should be compatible with at least Win2k, using a DOS command script employing the "FOR" command (I'm not sure about Win98 or ME's 'FOR' implementation).
::========================
::Use this DOS script ( .bat or .cmd )
::========================
:: traverse as high to your thumb drive's "root" dir as necessary
:: in my case the path looks like this: \apps\util-syncback, so I need
:: to call ".." twice to go up-folder 2x.
pushd ..\..\
:: parse off the current drive letter & "root path"
:: (nice for testing where you don't have the same directory tree
:: as on the deployed/live Thumb Drive)
:: the path will not include a trailing "\" but that could be
:: concatenated at the end with a \
for /F %%i in ('cd') do set usbbasepath=%%i
:: return to orig. folder/directory
popd
start syncback
::===============
:END
::===============
SyncBack will use the environment created by the DOS script, and a user can now create profiles that use the %usbbasepath% environment var that'll have a portable, but fully qualified, <drive letter>:\<path> parameters.
But really, there does need to be a simple file sync util. written that can use ftp, that can, independently of good time synchronization, determine the time offset between hosts and then CRC/MD5/SHA the files to determine deltas. Another thing I'm going to look at next is lightweight bittorrent clients and seeing if there's a way to push deltas via a functionally private bittorrent sharing a TrueCrypt volume.
Where there's a whip, there's a way!
/leeOne last comment, as perhaps an ounce of excessive caution, it's good to have some kind of UTC time synchronization utility handy on both the Thumb Drive & remote computer so that both computers reasonably agree upon the time of file creation, etc. Were I to script it myself I'd send a test file to the FTP server & then check my time against the server's file time and then check for time offset. I don't know how SyncBack handles problems like this, however, so it's good to know both machines agree on the time & date. If you've ever had Windoze munge up a person's roaming profile b/c of this then you know what I mean.