i've been using pdaxrom on my c860 for probably over 3 years now. its always been stable and fast, my c3000 i've been using angstrom on though, because their build environment is accessable, easy to get going, and updated between releases (not that they have any "stable" releases yet), so i have experience with how to port packages from openembedded to pdaxrom.
but enough off topic.
the point of that is that i've been using e17 and a 2.6.22 kernel on my c3000 for over half a year now, and am finding the kernel and window manager very effective. if people are interested in videos or other information related to the responsiveness of e17 i'll gladly provide what i can.
the positives of e17 as i see it are:
Very easy to remember window position / virtual desktop settings
Low processor usage eye candy ( not required but fun to show off)
Good centralized management of configuration options (everything gui related can be configured through the main interface, including changing default font sizes of different wm aspects, titlebar, and scrollbar to name a few that apply to pda usage. they help with easier finger dragging and scrollbar usage)
(tenative) some work has been done doing an iphone type keyboard based off e17 libs, keyboard looks pretty nice, but its not fully implemented right now. it would be a really nice feature though.
Actively developed
some negatives
there aren't that many epplets (their version of a taskbar app) for e17 right now, so volume, brightness, cf/sd, wifi epplets would all have to be written. there are lots of example epplets in the e17 repository though.
i can't really think of any others right now, so how other people see it would be appriciated.