thanks for the replies. i've closed the program on 32 weeks for now. the size of block folder (%appdata%\Bitcoin\blocks) is 5.32 GB, but i'm sure it has used more than 15 GB of internet traffic. where has the rest of it gone?! please don't tell me to check my firewall or other app usage, i know it for certain! is there something like "wasted" in Bittorent?
It's possible you're acting as a "seed," passing on the blocks you've received to others. There's no way to limit how much bandwidth is used to share blocks in the client. If on Windows (unsure of compatibility on other OSes), you might want to consider an application like NetLimiter, which'd allow you both to limit UDP activity in Bitcoin and monitor how much bandwidth the client's consuming (it provides graphs for data collected over time, too -- practically essential for anyone on a capped connection to determine where the bandwidth hogs really are). For reference, the Bitcoin client shouldn't need more than a 1kb/s upload allotment to download the blockchain. Netlimiter's useful in quite a few other applications, too (I've been looking for a FOSS alternative for doze, though, if anyone knows of any).
If it really is downloading that much for so little good information, there's probably a problem with a peer sending you loads of bad data, or a RAM/HDD/connectivity problem on your side. It'd be interesting (and maybe useful) to learn more - but for your sake, you might want to consider using a lite client like Electrum.