Maybe some people need to hear a message of "hope." Some people have had more than their fair share of heartaches, sorrow, and loss in their lives, even though they are born-again Christians. Joel Osteen is the very first to say that his primary ministry isn't evangelism, it is ministering to the Body of Christ, yet, he always gives an invitation at the end of each service.
As far as
his theology goes, the Bible Study material offered by Lifeway which is probably taught in most SBC churches on Sunday mornings is what some people (like me) would consider pablum, not meat. I have run into quite a few Southern Baptists who don't know much of what the Bible says about anything, just for the record (being from IFB background myself), but now a member of a SBC.
Not trying to hijack this thread, but to point out that different people have different needs at different points in their lives. Sometimes people have had so much heartache and loss, they need to have hope that Romans 8:28 is still true, that God does have a plan for our lives, that we can't give up when we feel like all is futile.
I have never heard Joel Osteen preach anything that is out of align with the Word of God, and I believe I'm pretty well grounded in God's Word. And he never asks for money like a lot of televangelits do.
Most of us already know what sins we are guilty of and our failures, so hope is nice to hear once in awhile. It's not itching ears. Joel Osteen is just reminding people of the "goodness of God" like it says in Romans 2:4 - the "goodness of God leads to repentence."
Edited to direct you to this thread - 60 minutes Interview with Joel Osteen (in the News Forum):
http://www.baptistboard.com/showthread.php?t=50620