1. Requirement to convert to 64 bit infrastructure.
2. New features generally are Ajax reworks of existing features, that people are used to.
3. Sudden loss of IE 6 support.
4. People are not yet using SharePoint 2007 to its full potential.
6. Lack of downloadable VM that can be easily run on most 32 bit dev machines for learning.
In a word, I can't show SharePoint 2010 on my work laptop, I can't view it on the IE browser that is the company standard browser needed for all our Oracle and custom apps, and once I get it running most people can't really notice any difference.
I fear that, just like Vista, the overhead is far far to great to make the upgrade worth it and we may have to wait until SharePoint 2012 (SharePoint 5) to get any real upgrade.
But don't fear. Microsoft is wonderful at getting itself out of messes like these.
But I will have to take back my 2010 only promise. For the time being SharePoint is SharePoint 2007 and I will have to keep writing about this for some time.