I've written pretty much every day for 40 years. rMBP is the best writing implement ever.
I back-to-backed this issue as follows... When the rMPBs first came out, Apple had not yet updated iWork to retina resolution. I went to the store many times to test non-retina Pages on rMBPs. When Apple updated iWork, I returned, and continued testing, this time typing in the (new) retina version of Pages on rMBPs.
The difference is night and day.
And the same observation applies for Pages on a MBP vs. retina Pages on rMBPs...vast improvement in the retina hardware+software environment.
Trust me, if you're on your Mac (like I am) 10 hours a day, a lot of the time reading and typing, writing, editing, rMPBs are a godsend.