A few answers...
-> Note that I have yet to find a GPS software package for the PDA that includes both driving and hiking maps. You're most likely looking to make two separate purchases here whether you want to or not.
-> I'd look for past frequency of updates, the types and quantity of hotspots (gas stations, emergency stations, restaurants, etc) listed, as well as niceties such as phone numbers included. Some also include live traffic conditions if you have an internet connection...always a plus.
-> Updating the maps is easy, and most will offer free updates for one year. Look to spend at least $50 for map updates thereafter, and those are limited...you may have to upgrade the software to update the maps. Check their policies before buying.
-> Yes, you can hear/understand the spoken directions, provided you don't have it in a case/pocket/purse or the radio up too loud.
-> Directions vary widely between services and location. In larger cities where road construction and business openings/closings is more of an issue maps become outdated much faster. One tip: Go to your local electronics store and try some of their standalone GPS units from those companies. Enter some sample routes you take daily and see how accurate they are where you live. The PDA versions use the same maps, so it's a good way to see which one suits you best.
-> Support varies widely. TomTom's generally good, Garmin slacks off now and then, CoPilot's OK, and I haven't dealt with Delorme.
-> Remember that 4-hour battery life! That's why PDA's don't make good GPS units unless you have a car charger and/or extended battery packs.
Hope this helps,