I have been using it less than a week and it is my first GPS device.
I bought the device + all Europe maps from supergps (454 inc, next day AM).
I was very happy with them, but Citylink delivered at 11.52am of course.
It picks up a signal very quickly, sometimes in 5 secs after starting MioMap & on occasion, in GPSdash2, the satellites pane is full in about a second!
In the car it works fine, on the train for fun (!) a little less, but still works.
In building, not so great (obviously). I read somewhere somebody had a signal in the glovebox. I believe the SRIF (GPS) chipset is a version 3 which is much more sensitive.
I have not had problems understanding the MioMap interface (immediately I made it 'extended' i.e. expoert mode. The lack of full UK postcode inputs has not bothered me as you can still put in the first 4 digits & then the next line gives you a selection of roads & then asks you for the house number anyway. NB I am about to buy a 2gb card to fit the entire Europe map on (1.6gb) which avoids a MioMap software reset between ind. 'region' maps e.g. UK, France, 'The Alps', Germany etc. which are about 200-300 mb each.
The bundled kit in the box was the biggest set of extras with a PDA I have seen, including windshield mount. The lack of WiFi you can solve with a Spectec 802.11g card from Expansys, but I do not do much Wifi surfing as I have a 1kg laptop for that (1280x600 beats 320x240, the latter I find just too small).
The design is good and I find very aesthetic, and the machine was a lot smaller than I expected, although I guessed it was JAM sized, but the fact it has a full GPS that I have found to actually work, whilst hiking, is quite outstanding. The WM5 Mio skin works well in black. I have been through all the setting your own skin, background etc, but I will just live with this one, it is good enough. Also, Activesync 4.1 has so far worked flawlessly, but I do say that I did install it on a fresh XPpro installation (which did not have any Activesync on it at all!). That was due to my yearly reload of XP (which everyone must do unfortunately, I did not believe it, but now I regularly reinstall the O/S via fresh Norton Ghost images).
The main disadvantage is battery, but with careful setting, I think you will get at least 6h in the hand. In the car, the bundled cigarette lighter charger = no hassle (really, I am amazed at the extras bundled = leather belt case, wall charger etc).
Good luck with your research!