I have been 'user testing' a D50 for the last four weeks (Sony Store has a 30 day return policy), here are my observations
Pro
Sturdier build than many other handhelds
Ridiculously long battery life
Great display, fast VU meters with peak indicators
Intuitive and easy to access interface
Pre Record buffer(didn't use this though, and using it without a remote might result in an audible click when you actively start the recording)
A-B mark looping
Digital Pitch Control
Interesting limiter, but didn't spend too much time testing it
Easy file splitting
Clean high gain preamps
Sensitive and detailed internal mics with very good sound
Headphone amp has excellent sound
Digital input
Big but still pocket sized
Con
Non Robust 1/8" connectors (although the headphone and mic inputs are beefier than the rest)
No phantom power or XLR
Internal mics sound 'bright' (take phones on and off while monitoring recording, big difference in sound)
Internal mics VERY sensitive to wind or even recorder movement and handling noise
Memory stick (not a huge problem)
No mp3 recording for quick and dirty files without having to convert later
No separate gain controls for L/R
Took the D50 back to the Sony store today, felt queasy afterwards.
I had a FR2LE out over the same time, overall, it is much more primitive, and somewhat larger (no sticking this in your pocket). It doesn't come close to many of the 'pros' of the D50, but it sounded equal with much and slightly better with some of the material I recorded. The most a/b'ing I did was with recordings I made with a rented pair of Rode NT1A's in front of my relatively high end stereo system. Not the ultimate test I am sure, but to compare 'voices' of the two recorders with a consistently repeatable source, it seemed instructive. The D50 sounded great, but the FR2LE just sounded a bit more dynamic and open. I need to make the decision to keep the FR2LE, or keep lookng, over the next few days.
No experience with the R09HR or the Zoom, but wanted to share my thoughts on the D50.