sgould, you will be pushing it as far as amount of starter for each brew. i'm sure it will be fine, as you can technically just pitch the smack pack for one 5g batch, but normally, you'd want an entire 1L for each batch (depending on your OG). again, if you've already got two batches in the works, just split it and let us know what happens. you'll still make beer, but you might get a few extra esters as the yeast will have to reproduce more than they would if you pitched the proper amount.
HHB, don't let 'activity' fool you. is there a good amount of yeast settled on the bottom of the starter? was it a stirplate starter, or just shake it when you think about it? a lot of times, starters seem dead, but are, in fact, quite alive. i wouldn't let it spoil your brewing plans, just pitch it. worst case scenario is you have to drop some nottingham or another pack of yeast into it. even if the pack was already smacked, it shouldn't affect the viability of the yeast... but you say it was a propagator, which isn't a smack pack, those are activator packs... how old was the yeast, where'd you get it from, and how was it stored before use?