I posted a while back about possible improvements to the Gmail system. Here are some additions to that post.
Nested contact groups
It would be nice to nest the contact groups. I doubt that many people would use this feature but it would be easy to implement for those who would. I would like to set up a hierarchy of groups so that I could place contacts in granular groups that would reside in more general groups. This way I could send messages by using any group in the tree.
Notifications for outside newsgroups
For google groups, I would like to be able to receive individual emails from newsgroups that are not registered as a google group. I currently subscribe to a number of Microsoft, Cisco, and wireless newsgroups such as microsoft.public.cert.mct and I can only receive digest emails or no email at all. I tend to not read every email that goes through and I filter by scanning the subject lines. I cannot do that if I am using digest email so many times I do not even read the digest. I also like to respond promptly when messages arrive and I know that those who are using a newsreader are receiving each individual message instead of a digest.
Collaborative work environment
I would like to see some sort of groupware, collaborative work environment product from Google. I envision an online site where I could share documents and other data for users to edit. The system could be similar to SharePoint and other groupware software available now.