I've used every version of REALbasic since it's inception as CrossBasic -- for the purposes of full disclosure, I have been employed by RS in the past. While there have been ups and downs with Rb in the past, it has consistently met my needs as a software developer -- with the possible exceptions of the IDE rewrite of 2005, which introduced some major growing pains.

However, with 2006 R2 and now 2006 R3, I think the dust has finally settled and the future is looking good: As a long time user, I have finally been able to move from version 5.5.5 to version 2006 R3 and be as productive as I was before.

A few things to be aware of: Universal Binary support is not yet implemented, but according to RS it is scheduled. The IDE has many multi-window improvements in R3, but the debugger does not yet support multi-windows for variable watching/debugging. Performance also seems to be a bit more sluggish over 5.5.5.

Despite the shortcomings, many of which reviewers have echoed here, I think Rb fills such a unique niche compared to the alternatives (XCode, CodeWarrior, .Net, RuntimeRevolution) that for me, it has no other competition at the moment. Every development environment has pros and cons; I think it really boils down to what a developer feels comfortable working with and whether it fits their needs. Rb has met those requirements for me for close to a decade now.