LOTR:

1) See Roger's reply.

2) The VM issues on OSX are purely Apple's problem. We unfortunately can't do anything about it. I hear Tiger may have fixed it.

3) Not sure what you mean by this. Magnet links that only have a SHA1 still will not start downloading automatically, but they will create a download. I think LW now gives a notice that you need to start a search.

4) Yes. As Zlatin mentioned, the 4.9.0's "saved downloads" format is not compatible with prior versions. It can read older ones just fine, but older ones cannot read it.

5) Incomplete files will stay for just as long, or as short, as they used to. I believe that entirely depends on what setting you've put in the options. While the incomplete file is around, though, LW will remember more possible hosts for connecting.

PSes) Yup, loading shared & incomplete files is faster. We optimized a LOT of stuff.