yes, i have the R4M and have had the pleasure of using it for the last two weeks ( with the new 21/4P - the 21/4 in M-mount).
There are some cameras that are "moments of truth" in a photographers life. the first time i held an m2 with the 35 on it, my first Nikon F and the leica MP with the 0,58 finder. The R4 falls into this category! If you are a wide-angle shooter, it is an "epiphany" camera. It just fits in your hand and view. For the trip to Japan I took a M2 with the VC 40/1,4 MC, a R3M with the 75/2 Summicron and as i knew that i would get the R4M and the new 21/4P once I got there, it was an unusally light travel pack for me. I did include a 12/5,6 for a specific shot (the shattered dome at Hiroshima Peace Park). Of the 45+ rolls i shot, about 25 were shot with the R4M. It is a spectacular finder! With the 21 I can see the framelines with glasses on. There is a faint reflection of the frames off to the side of the finder but not disturbingly so. Shutter noise and feel is the same as on any R3/R4 body. Slightly "clunky" release, which is a function of the shutter. Advance is very smooth and rewind better than on my Zeiss Ikon? All of this pales when looking through the finder - it is crisp, clear and sooo wide! So far I have only been using it with the 21/4P ( Mt kobayashi said, when he gave it to me" Oh, I hope you dont mind that it is a pre-production lens! The full perodsuction run wont start until next week!". No. I did not mind at all! It is the same formula as the screw-mount version and as that is one of the best 21's that you can buy - why change. The aperture ring has the "ears" of the 35/2,5 II on it and it makes it easy to set and change aperture.
The 25/4P will be out in late April and I have been promised one of these, once it is out.
All in all, the R4 is all I expected it to be and more! Combined with a R3 you are covered from 21 to 90 mm. I suspect that my new travel pack will be the R4, a M2 ( still a great camera) and a R3. the 21, the 28/3,5VC, the 40/1,4 and the 75/2 Summicron (best finder for that lerns is the R3m).
I did run into Mr Ho at Lemon camera and we had a great talk and as he said, he got a bargain 25/4 for less than $100! I must admit, that if he haden.t bought it - i would have. although i already have a couple of them!
Apart from the R4M and the 21/4P i showed remarkable restraints and only picked up a Canon 35/1,8 LTM and a couple of hoods (i am always looking for these) for a 105/2,5 and my old Biogon 21/4,5 as well as a repiica "minifinder" for 35mm for Nikon Rf. original ones are $1500+ and at less than 10% of that, the replica looks good. It is just as bad as the original so it is more for looks than anything.
For those of you who are waiting for your R4's - it is worth it and for those of you who are wavering - if you like using 21/25/28 and even 35's - just go for it!