I have a Roku and I LOVE it. It does, however, have its limitations in that it has no YouTube app. I like it better than my Blu-ray player that has most of the same apps because it's just so stinkin' easy to use. No boot time. Simple user interface. Just all-around a well-designed product.
Hulu Plus' usefulness is debatable. I like it because I can get HD to my TV thru the Roku with it. However, not everything availble via Hulu Plus is availalble to stream to your TV, and a lot of the content that is a benefit of "Plus" is duplicated with a Netflix subscription. In addition, several major networks do not have agreements with Hulu to host their content - CBS, TNT, USA to name a few, which really stinks. Hulu's free version will probably do you fine if you're willing to watch on your computer, especially if you already subscribe to Netflix, and using your computer will allow you to keep up with those other networks as well using their websites.
I still say get a Roku though. They're relatively inexpensive for the value they provide, and I just think they're awesome. Plus, their marketing is purple.