I just switched over recently, like in April. The learning curve took about a day or so to figure out the basics, and I am still learning some of the advanced controls.
I bought a Unibody Aluminum MacBook with the 2.0 GHz and 2GB Ram and 160 GB hard drive. It is 13.3", but I was using a Dell XPS M1330 anyway, so the size is roughly the same.
I immediately upgraded the Ram to 4GB and the hard drive to 500GB. They both went great, and had the Mac up and running in no time flat.
I also installed Windows 7 RC with Boot Camp, just in case I needed to use specific apps for Windows that I could not find for Mac, but have found enough to keep me from booting into 7 for that reason.
Some apps I use are Open Office to replace MS Office (still may get this later), Flip4Mac adds the ability to view Windows Media content on the Mac, as well as in Safari, Toast Titanium for burning CD's and DVD's and MS Messenger for Mac to access my Hotmail easily.
I may purchase MobileMe and change all of my emails over to that, but I am waiting right now, as there is speculation of a new version being released in the near future.
There is other software out there, but that is what I need for the moment. I usually look as I need.