[quote name='crunchewy']Hmm, so a memory card could be used to restart an Arcade game with your own gamertag? Could you then replacethe save on your HDD and thus start over on your HDD?
I ask because I'd read that arcade games couldn't be restarted due to your save data being on a server.[/QUOTE]
If you are redownloading an XBLA title on a 2nd system, I think the 2nd system needs to be online and you logged into Live to play it as a Full game and not a trial.
Some Arcade games store info with the gamertag. Others use a separate save (like PoP).
I just have both of my consoles on the internet, and save all game save stuff and profile to the memory card. even 64 megs is generally enough (though, rockband's profiles are pretty large). Then DLC goes to the hdd, redownloaded on the 2nd system (which can then only be used by my profile when I'm logged in; some of it can be used by another profile if I log in as player 2-4).
though, if you are shopping, i'd recommend the 512 memory card, specifically for themes, gamerpics, gamesaves, and games like bioshock add up