Apparently 5 GB is the gold standard for free cloud storage. That’s the maximum allowed by Apple’s iCloud, and possibly the same for Google Drive (which could be going live this month, so say the rumors). Amazon Cloud Drive also offers — you guessed it — 5 GB. That might be roomy enough, if your storage needs are modest. But anything more, and it’s just frustrating.

So when Dropbox announced its latest promotion this week, I was flat-out tickled.

If you’re not already familiar with the service, it’s basically cloud storage with a twist: Users can increase their storage limits by referring pals. Every time a friend registers, the originating user gets 250 MB of additional storage capacity. Scratch that — with this announcement, the DropBox bonus award doubles, going up to 500 MB per friend. Now that’s just nifty. Theoretically, you can score a mother load of cloud storage for zero cost.

Let’s do the math. The offer extends up to 32 referrals, so users can get up to 16 GB total of extra space. Add that to the 2 GB you get when you sign up for a free account, and that’s 18 GB. (Of course, things get kicked up a healthy notch if you’re a paid subscriber. For Pro users, each referral earns a whole GB.)

That completely spanks the 5 GB offered by the others (which is probably why DropBox took action now, in light of the GDrive rumors). But even without this promotion, I still find it to be worthwhile: The service can auto-sync to a folder on your desktop (which makes uploading dead simple — just drag it in), lets you share folders with friends, offers both online and offline access, and is available via mobile too.

Are you a DropBox user? Would you recommend it to friends? Tell us what you think of the service in the comments below.

[via The Next Web, The DropBox Blog]