Randomthoughts
Adventurer
I'm the opposite. As a player, I wouldn't see a need for DDI unless I really wanted to "get into the game mechanics" and/or optimize. A player could get away with talking to someone with a subscription and making the appropriate choices as they level.As a player, I love, love, love, ..., love, love DDI. It is far more cost efficient for me to have everything in one place. And WotC gets more money from me now (per year) than it ever did in the past. Plus my characters can be accessed in far more places.
As a DM, my feelings towards DDI fall to merely liking it. I worry about "renting" adventures and losing my Monster Builder custom material. (yeah, yeah, it doesn't "build" monsters.) For DMing, I would rather have a bound book or magazine.
The net value to me is totally positive. I don't want the 20+ books in my library like @Dannyalcatraz .
OTOH, I find DDI invaluable as a GM. I use the Compendium and Character Builder extensively (usually to help players with their builds). I use the classic Monster Builder a lot but look forward to more functionality for the online version.
I have most of the 4e books but really prefer the ease of online use.