I started using a 600 as soon as it was released and upgraded to a 650 once that was available. The Treo has been a part of my day to day life for several years now and I have been using it as part of my GTD system for about 6 months.
I have been fairly happy with the straight-forward outlook to palm conduits. I tried keysuite and thought it was acceptable, but not worth the rather significant cost: $70.00
One of my objectives is to keep my system as simple as possible and so I do not want to spend a great deal of time tweaking and adjusting my Treo to mimic outlook. I personally use the Treo as a reference tool (looking up contacts, checking NAs when the context presents itself, etc.) -- my use of it as an input device is more limited: email and calendar and occasional tasks and notes. However, I mainly use a levenger pocket briefcase and 3x5 cards for anything more than a few words since it is faster and more direct.
Bottom line: I suggest using just enough extra technology to run your system (i.e. I use snapper mail for email), but don't let the system run your day to day practices.
