Andy,
Which m42 adapter did you get and from whom, if you don't mind?
Jumped onboard with a Nex 5 on Monday and so far am very pleased. I use a mac and the software update went very smoothly. There have been some recent threads (elsewhere - not here) that have complained about the process on a mac, but I read over the guidelines first which are pretty standard, and had no issues (running 10.6.6.). Sold off my Canon dslr (again) as I was really only using it for sports shots of my son anyway. I was able to tryout a Nex for a couple days and it will be alright for my needs. I found myself going down the money pit again with the Canon gear/lenses and just decided it wasn't worth it for what I really needed it for. On the Nex with the ability to assign a couple of the hardware buttons to other functions, my earlier trepidation about the menu system are mostly gone. I was encouraged to see that Sony is planning on a future model that will supposedly incorporate more controls, etc. for the more advanced users.
Although I was ahead of the game after I sold off the Canon gear, I told the bride that this would be it for awhile. I don't think she believed me.