From the e-mail notifying me of my voucher:

This voucher is good until August 1st, 2003 (midnight).

So yeah, it's valid for a tad under one month, no longer :(

...and I checked. There's things I'd have bought with it (e.g. the Hydra, a ton of $1.99 PC products) but to spend it with their "gotyas!" I have to really scrape the bottom of the barrel :(