No more alts?

[Sevis]

For instance, I invited 12 alts to Dropbox to get the +3 gigs of uploading space. I registered all the accounts to twelve of my Uni library's computers and to 12 disposable e-mail addresses. But do not worry, the computers there save no data after I log off, not unless you stick it in a special personal folder.

Even if the mods did actively seek out those alts, registering on a different computer, under different e-mail should do it. Especially when the browsing is carried out from a different IP address (change yours/ cover it under a proxy).

You seem to rather misunderstand the technical side of it. What computer you register on is of no importance - you could have registered them all from the same uni computer. Similarly, the computers could keep verbose logs of all hat was happening, and Dropbox staff would know no more than they do now.
Where you register your account is another thing that is rarely kept - however, all browsing would have to be done from a new IP, if you wanted to pretend you are a new user. This could cause several problems (especially for 56kers, whom this forum seems very friendly to - not surprising once you see the name), as not everyone can switch or keep IP at will.

On the matter itself, a ban is a ban and I don't see why evading them should be allowed. An old user who has since that time matured, and wants to start from a clean slate is fine, seeing as he may truly act quite different, but a short-term ban has, imho, far more effect on behaviour when it is enforced.