When I subscribe to a YouTube channel, I do so because I want to watch basically everything they upload, or I at least want to have a clear view of new uploads on that channel. The best possible arrangement, for me, would be to have all new uploads from my subscription channels added automatically to my Watch Later playlist. For now, here's the best solution I've found:
Get an RSS Feed Of Your Youtube Subscriptions
This page describes how to get an RSS feed for all your subscriptions, which you can use in any news reader of your choice. I've added it to Feedly, which I use for my news since Google set fire to Google Reader. Anyway, it's a fairly simple matter of making your subscriptions public, finding your user ID and pasting it into a GData URL. It looks pretty good to me so far.
Mokalus of Borg
PS - It's made my subscriptions useful, anyway.
PPS - I like working with single feeds for similar purposes.