I know many other individuals are using Microsoft Project together with Clarity and wanted to discuss some things that I've discovered over the last year that may help.
Right now our organization is using Clarity with Project 2007 (soon to be 2010) and are users are struggling with dates changing in their schedule without understanding the reasoning. About a year ago CA came out and made some recommendations on how we use Microsoft Project and one of the largest changes was moving from the task type Fixed Duration to Fixed Units.
When I first started using Clarity at our organization we were doing duration based only scheduling and had no issues with date changes. When I moved to resource loading tasks I began to have unexpected results. The most interesting part was that dates were still changing even when actauls were not being applied so I investigated further.
What I discovered is that Clarity is not functioning with Fixed Units correctly! In a scenerio where I have an employee who is dedicated to my project full time they would have a max allocation of 100%. Let's say that same resource is working on two (1 week duration) tasks at the same time. That resource should be working 20 hours on both tasks and be allocated at 50% on each task so their total allocation is 100%. This works approprietly in Microsoft Project but when you save it up to Clarity and bring it back down again the duration has changed. Upon further investigation the duration changes because the task level assignments went from the 50% we gave them to be replaced by the max unit which is 100% in this case.
Why is Clarity applying the Max Units on to the task level? Why can't it leave the task assignment level units alone? By doing that we could see when individuals have overscheduled a resource without Microsoft Project automatically changing their dates.