When IBM announced the Public Beta program of Domino Designer 8.5 the code quality was so bad that it was hard to make anything useful with it except maybe XPages. Later on if you report something you most got the answer that this problem has been fixed in a later build (which was not public).
Now that the final is available I must say that I would really like to love Designer 85 because it has many new possibilities. Unfortunately everything that IBM has thrown out on the client side in the Notes 8 product line stinks and so does Designer 8.5 Eclipse. It is slow and it is buggy.
Focus issues, Design elements just don't open no matter how often you click the mouse button (pressing for example CTRL on the keyboard seems to help sometimes) and strange error messages.

I know that the Lotus community is forgiving almost everything but from my opinion a 1000$ product deserves a better code quality. Sorry for me this is a Release Candidate, nothing more nothing less.
Maybe a comparision with Notes 6.5 is unfair because putting Designer on Eclipse is a huge task but as a customer should it really matter?
I will stay with Designer 8.5 for now because the bugs are annoying but not critical.
I can't say much negative about the Domino 8.5 server. All upgrades (5 so far) went smooth. You should be aware that upgrading a 8.5 beta server to the final code will probably break your server (it is not supported anyway).
Of course you can remove anything but keep the databases.