Hi I think your themes not bad, the only major critism I've got is it is quite a big download for a theme over 30MB.
So I've optimised all the picture files for web display, this will be a big benefit when alot of people access webmail using this theme on the one server, as bandwidth will be used up alot less. Granted it wouldn't matter as much if the server is accessed from a local network, but will matter if being accessed over the internet.
Also I couldn't help myself and I've changed the unfocused colour on the mail message screen for the " messagelist tr.unfocused td " to a light grey more in keeping with the theme than the tangerine orange used before.
Also changed same thing on the address screen "contacts-table tr.unfocused td".
Both things are altered in their repective css files, if you don't like it don't use it.
Regarding the login screen, I've looked at your 3 choices, although option 3 is the favourite ( a bit boring ), you could use option 2 it would work better by getting rid of the grey box that the login controls reside and having all the text and login boxes sit properly within the cloud image (might give the login page a fun element).
option 1 is too crowded with the icons either side.