Do it -- do it -- do it all day, and twice on the weekends. Take Brown, if you can get him.
Downside? Ummm, let's see: your starting RB's are MoJo and Pierre Thomas; your starting WR's are Andre Johnson (
*cough* coulda been ours instead of CRog
*cough*) and either a top 5 WR from last season rounding into form (Marshall) or this year's beast.

(I know -- I actually put in a waiver claim for him, and was relieved when it was denied.)
Your bench is Donald Brown (presumably -- Coffee is dinged up, and Gore is coming back) and either Marshall/Manningham. Thomas had his bye week last week, Brown has his bye week this week, Marshall & MoJo next week, Manningham & Johnson in Week 10.
Eeewww. Don't know how deep your bench is, but you have 2 WR's out in 1 week. Given that it's week 10, I'd still do the deal without compunction -- just plan who you're gonna drop and who you'll pick up for the week.