I've got the U42S.
Demos I've recorded with it are on my band's myspace so you can have a listen for an idea of how it sounds and what levels are possible -
http://www.myspace.com/thebaltics
I've been really happy with it. I wrote a review on it under another topic so I'll copy/paste and update where necessary:
Comments
I have recorded a few rough demos for my band using the U42S. All I can say is that I have expereinced none of the problems that other users have reported. I am operating Vista 32 Bit and I made sure I followed all the installation instructions properly and downloaded the latest drivers and I was able to start recording with Cubase almost straight away.
The level monitors on the U42S are helpful and are more accurate than I had been led to believe. The fact that you can press a button to link inputs 1 and 2 or inputs 3 and 4 so that they can be monitored directly and recorded in stereo is extremely handy and I would hate to have an interface without this feature as I am monitoring my inputs directly and recording stereo sources (keyboard).
The knob to slide from direct monitoring and playback is also useful and is great when overdubbing tracks. I would say that the recording loudness is totally ample for my needs and if you listen to some of the recordings on the below link you will get an idea of the level you can get without clipping.
I agree with come other people's comments about the gain being very bunched up at the upper end of the control, and there is a little bit of noise at the highest gain, but the highest gain would peak anyway so there is no need to put it that high.
Software
There haven't noticed any latency when overdubbing tracks. I have been switching between Cubase and Reaper (free download) and have yet to decide which I prefer. The instructions for using Cubase with the U42S are to set up a mono recording project, but the problem with this is that I am recording a stereo output instrument - my keyboard - so I find myself having to create two tracks and pan one 100% left and the other 100% right or else it sounds really muddy. There is decent editing of individual tracks or segments of tracks. The effects are decent and I have made a bit of use of the reverb and I have tried to use the compressor with limited success, but that's down to my inexperience.
Reaper is handy in that it allows me to select inputs 1 and 2 on my U42S as a single stereo source so I can record and edit my keyboard in one track. However, there is no way to open a single track in a separate editing window to, for example, silence parts of that track etc. The reverb seems decent too for vocals but it is slightly harder to get it to sound good than on Cubase.
I posted some recordings on my new band's myspace so if anyone is interested they can have a listen. If possible though, try to avoid using myspace comments to tell me how poor the recordings are
I would definitely recommend the U42S.