In terms of actually helping you today, the best plan I find is to only synch folders you really are likely to need local access to, and then set all folders to online only, and set a whole project folder to available offline each time you change project. doing it file by file you have to hunt down too many lost Gb's too regularly I find.
but for the long term... if you are on a mac...
Try NOT updating dropbox, so you can continue to use the older version and the best reason for Dropbox to exist which is external storage. Once you upgrade to the lastest version make sure that 'auto renew sucscription' is turned off, so when you inevitably realise Dropbox is now superflous to your needs you don't accidentally continue paying for the service. Once you are on the new version you will never be able to use (at the same time) more files than your local hard drive has capicity for. You will be in a continuous loop of make online, make offline with every project you want to work with. Dropbox are trying to make out like this is a transient problem they will fix, but it seems like they really aren't going to, and Apple doesnt want them to as it means people will start paying more for their storage upgrades when purchasing machines, and/or start paying for iCloud storage instead fo 3rd party options.
I'm hoping DB will chime in here with news that they have in fact worked out a way around this problem...?
