The biggest issue I have with the Treo is not with the treo, but is with my cellphone provider (Telus) the Data plan is still WAAAAAAAAy to expensive. $25 a month for 4mb. You can burn through 4mb in about 5 minutes of being connected to a IM server.
Some of the features I'm using that are new (to me anyway) are Facebook with the new client from Palm, and let me tell you, it's great, the client is fast the pictures download and upload quickly and it's easy to blast a couple pictures from the camera there. Another new (to me) feature is the wireless syncing discussed above, and the new version of Mundo messenger works great on the 755p!