I have to admit that new format did not bug me much, although indenting the posts is a bit distracting (as someone else also mentioned, I also just thought that there was ‘bug’ in formatting).
I might be a bit slow but what does this mean “the first message of a homepage post” – homepage of the whole site , or homepage for each forum (where post titles are listed), or homepage as in first page of each thread? If it is latter, I am not sure why do you want to emphasize first post – this site has good navigation, so it’s very easy to find out what original (first) post question/comment/etc. is.
So to summarize, in regards to formatting change: I am not fan of indentation, although I can live with it. It was distracting to me because it was different from what I was used to (both here and other forums). When I first saw it, I tried to figure out why it was different, what is so special about it, and is there any significant purpose to it. Granted all this took a second, however I did not start reading content right away (something I wanted/expected to do). And on top of it all, I came to a conclusion that formatting was off.
As for model change, I can’t offer any constructive comments, as I am not clear what you are trying to accomplish.