Memory
I am very happy with Lion but the only thing I have noticed is that my RAM isn't reallocated quickly enough and sometimes requires being put into sleep mode. I say sometimes because the only time I notice it is when I run VirtualBox.
Maybe it's just a case that you haven't noticed some of the bugs ;-)
Memory has been an issue for me. I have 20GB memory in my Mac, with 10.5 and 10.6, I never had any page outs. My workload hasn't changed, I'm still doing the same kind of jobs, and yet with 10.7 I have frequently had memory page-outs.
Unless you monitor this kind of thing, it could slip past many users.
Even simple things like watching HTML 5 videos is a stuttery experience, and yet my iPad can play them with a fraction of the hardware.
I am very happy with Lion but the only thing I have noticed is that my RAM isn't reallocated quickly enough and sometimes requires being put into sleep mode. I say sometimes because the only time I notice it is when I run VirtualBox.