Yes, no problem doing Silver Falls as a day trip from Portland; I've only ever done it as a day trip and I live here. Nothing else pops to mind as to what else you could do on the way home, but perhaps someone else will offer you something.

Some non-outdoorsy suggestions: There are some outlet stores in Woodburn off I-5 if that sort of thing appeals to you. (It's a big deal for some people.) Also, Fry's Electronics in Wilsonville is sort of a nerd's paradise with its great selection of computer stuff and electronics; if by chance you don't have one where you live, I can imagine some people really being excited about that. Perhaps not you. No sales tax in Oregon, though...

If I tell my husband, he would definitely get excited about Fry's. Maybe I won't tell him because I can imagine him wanting to spend hours in a place like that. Thanks for the info on Silver Falls. I'll include that as a day trip.

Andrew--LOL, yes Fry's is a big draw for some people. DH and I cringe when we have to go there though.

theatrelover--If you do go to Fry's, bring lots of patience with you. It has a lot of stuff, but isn't a pleasant place to shop, IME.