Generally this is very nice feature, thanks.
(3) But try set 'Host time' mode for Clock element for templated screens without selecting Parameter field and save. In bottom of page see error in editor and also in view mode (Monitoring -> Hosts -> Screens).
(1) I think for templated screens this Parameter should be hided.

(4) For not templated screens need to check user select this parameters or not before saving. Try to save without selected host now.
(5) And in pop-up window need filter to real hosts only without templates.

(6) And second serious new problem - now after save element is not updated on screen immediately. It need to click something and return back or refresh page to see changes. The same behavior for column, line add/remove.

(7) In Monitoring -> Hosts need to add single space symbol between Hostname and DNS-name.

(2) And not related only to trunk rev 14910 (something early revision):
In not templated screens "Hostname:" is not presented in Parameter field if you open elements (Simple graph, clock and maybe other). It presented for element Graph and maybe other (but only after save and open element settings again). Try to choose Graph, Simple graph then save and open again and you will understand me.
If you open pop-up window for host selection and try to change host group then you receive error "Warning. Field [submitParent] is not integer".

heh