The first thing you should understand is the plugin model for feature development is very simple and the main integration is at the UI level so there is no limit on what you can use in your own custom development in terms of busines logic or data access. You don't have to do things the way I do them. If you like SubSonics, or LINQ, or NHibernate or whatever, there is nothing stopping you from using those things.
Myself, I do not like OR Mappers, I like straight forward sql code optimized for the specific db. I breifly became enamored with SubSonic because I thought it would make things easier to support for the non MS SQL data layers. But I found it added a lot of overhead and when there were problems it was much harder to debug my way through the subsonic code. I went back to just using Codesmith to generate standard dal code for each layer as a starting point for feature development. Its only a little more work on the front end to implement a true db specific dal than SubSonic and its easier to fix things because I can just go right to the sql when there is a bug, and less resources are used at runtime. As I've said, I think SubSonic is still useful in terms of developer scaffolding but I have no plans to use it going forward for production feature code.
I also have no plans to use LINQ to SQL or Entity framework in my own work.
For your scheduler project, you might want to look at DayPilot as something you could use in the UI. I used it in my new Event Calendar Pro product. The dll for the free open source version of DayPilot is already in the mojoportal solution in the _libs folder.