I signed up for the BBC iPlayer beta, and got an invitation to join it in my email inbox a few days later. It's a bit of a faff to set up (they assign you a randomly-generated - and hard to remember - username, and you then have to sign up for a separate BBC account too), and of course it only works on WinXP + IE6/7. But it seems to work pretty well on that. I had no trouble downloading an episode of Adam Hart-Davis' excellent Beginner's Guide to the Cosmos that I'd missed.
The DRM is (to me) rather draconian; fortunately, it's a piece of cake to remove it at the moment. Just download a copy of FairUse4WM. I found it here, though Google shows up plenty of links. I won't directly link to it, since there seemed to be a lot of broken links - hosting providers getting jittery about hosting it, I guess. Make sure you check the MD5 (I use md5deep). Then just run FairUse4WM (it's a Windows program) and it'll strip the DRM from your iPlayer WMVs (though you'll have to find them - mine were kept in C:\Documents and Settings\All Users\Documents\My Deliveries, and there's no option to change this), quickly and easily. Voila! You can watch them, burn them to DVD, keep them for as long as you like - just like you can do with any DVD recorder right now. Fair enough, I reckon. Apparently that works with Channel 4's 4OD service too (it's the same underlying software), but I haven't been able to get that to work yet. I'll try a bit harder when I miss something crucial on Channel 4.