I guess I'm reasonably new to the forum compared to many - I've been on here around a year, and bought 2 machines I'm extremely happy with. Also I have donated each time despite not being required to as a buyer, but happy to contribute in a small way towards the costs of running the site, which provides a much safer and more comfortable environment for buying machines than the likes of eBay, Gumtree etc..
My comments, for what they are worth are:
1. The classifieds are a new format, so will take a little adjusting to, but I feel that this is just something that will take a short time, so not in itself an issue. At the moment, I admit I find it a little counter-intuitive from the forum home page to locate the actual machines for sale, and maybe this could be improved especially to make it easier for new members. For regular forum users, it's not difficult to save a bookmark.
2. The question about people putting "PM sent" on a thread when sending a PM, I feel is useful in that it registers an interest and forms a record of the order in time that people have registered that interest. The rationale being that (all things being equal), sales tend to go on a first come first served basis. I think that if the first respondent can't come to an agreement quickly, then the seller can easily indicate the machine is still for sale, and given the general level of interest in machines for sale on here, it's not going to add much delay or otherwise compromise the sale.
3. Discussion on for sale threads generally seems to be useful, but I do agree that people who just post their curt negative opinion on the game theme generally are not helping matters, but these do seem to be in a minority of cases.
4. The main issue I have with the new setup (as has been mentioned) is that when looking at sold machines, the price does not seem to be available. Again, from a personal point of view, I think it would be very useful if sold listings included the sold price. This would provide a useful reference both from a buyer and seller perspective as to what similar machines have gone for in the past. Obviously this only forms a rough guide, but from a personal point of view it would potentially have prevented me from making a silly low initial offer on the first machine I ended up buying!
All the above are obviously only my personal opinion as a relative newby on here.