for DVD queries i would go over to
www.thedvdforums.com
RCE is basically a system which was introduced by Warner last year on it's Region 1 discs to stop us with multiregion or regionfree players from playing discs before they are released officially and it is basically to do with how the disc checks the region settings of the player
of late it has mainly been Columbia Tristar who have been using RCE on most of it's major US releases (such as Charlie's Angels, The 6th Day) - although Columbia seem to be making an effort to make the R2 versions of RCE discs (and most others) as good as the R1 so there is less reason to import (apart from getting them earlier - both the discs above are out here anyway and as good as R1 - The 6th Day is actually better)
as far as i am aware, most multiregion players are fine with RCE - if you switch Regions manually you should definitely be ok with RCE titles, if you only have a mod which automatically switches region you may have a problem depending on your machine and what make of modification it has (i have a Sony 725 with auto-switch only Tridek mod and it is fine, but other makes of mod which are auto-only do not work)
unfortunately Pyara, i think Toshiba machines with auto-only switching were some of the worst affected by RCE, although most recent auto-mods are now RCE compatible (and most mods now have both an auto-switch
and manual region switching option)
the sure way of checking if your machine is RCE compatible is to check it with an RCE disc - the only other titles i can remember having RCE are Hollow Man, The Patriot and Thomas and The Magic Railroad (really!) - but if you look on a R1 DVD retail site they usually state which discs are RCE encoded (although some sites sometimes tend put it on all Warner/Columbia discs as a precaution)
however, if you are affected there are usually ways around the encoding, eg. directly accessing titles/chapters by keying them in rather than using menus (check out the link above for such info)