Right, don't sign up for anything pay as l_macd said. When you first sign up for those 5GB, you'll get an extra 500KB if you use my link (I do as well), plus you'll earn another 625KB for completing certain tasks after signing up, like sharing a folder, installing the software, etc., giving you 6.1GB to start out with free. And it stays totally free, it doesn't stop after 30 days.
I'd create a 2nd free account rather than pay for the storage. And if you need a lot more space, Copy works out very well for the PC and downloading to my phone. The browser on the Kobo Glo just doesn't work very well with the Copy layout. And with Copy, getting friends to sign up increases your free space by 5GB per signup, and I don't think there's any max cap on the free amount you can earn there (in fact, someone posted they have over 250GB free space so far). I use Copy for uploading my photos, especially while I'm out of town so if my Netbook dies or gets lost, I don't lose anything after I transfer pics off my camera nightly.