It was not long after HP finally released the Windows Mobile 5.0 upgrade that we started getting feedback from people who had done the upgrade. Much like what Dell X50 users went through a few months back (and are still working through), the hx4700 upgrade has not been without its issues.
Mobility Site has a nice roundup focusing around the Windows Mobile 5.0 upgrade for the HP iPAQ hx4700. They have a poll that looks at whether the upgrade was worth it and a video that shows WM5.0 performance after some tweaks. Best of all is a forum thread that might help you do your own tweaks to improve performance. Just remember to exercise caution if you play around your registry!