Vista looks a mess
Vista seems like it will have brain-dead security, which gets in your way, causes confusion, blocks rightful use of media, breaks application and blocks proper security software. Microsoft seem clueless about proper security (e.g. the critical need for egress filtering). If people have to turn off the extra Vista security, or hack around it to get work done and have proper security, then the extra Vista security is worthless!
As for .Net, you limit yourself and your software to the increasingly expensive windows platform (I doubt Mono ports will be viable), when many Enterprise applications run much better on cheaper/faster Linux, (Open-)Solaris and other OS platforms. All my own and work projects use Java and work fine on many systems, I don't see enough benefit in the .Net features to justify the lock-in, so regard .Net as irrelevant. If some Vista tech proved useful, I bet it would not be long before it gets ported to XP and Java, given that some Java GUI libraries and Windows shell extensions already emulate some Windows Vista features.
I currently use a locked down XP Pro and apart from a few glitches I very rarely see any security issues, given that Mozilla software, my firewall router, third party firewall software and use of restricted acounts protect me against the kiddies and criminals.
IE7 looks like little too late, Firefox and Thunderbird already have very good RSS support (as standard in Thuderbird) and are not standing still (the extensions scene is quite active), so it is doubtful that IE7 will ever catchup.
In summary, I think Vista will pan for most XP users, given that it does not offer enough improvement and has many downsides, like more usage restrictions and the requirement for a much more powerful computer, to be usable.