For me it is a must have - it was one of the main reasons I chose the Loox N560 (tough choice with the Dell X51).
I would be very tempted to jump to a more converged device if it had:
1. GPS
2. VGA display (at least 3 to 3.5")
3. Small and light enough (allowing for 2.)
4. Bluetooth
5. WiFi
6. GPRS minimum
However, if battery life is to poor, it's no big deal to carry a small, cheap GSM phone as a backup (or an extra battery - like the external ones that take standard AA).
Interestingly, the reminds me. I bought an external battery pack for my Loox the other day. It is a plastic box with an on/off switch, takes standard AA batteries (best to use NiMh, but can use alkaline, etc. if needed), and has a standard plug at the end. The pack is supplied with an adapter to fit the Loox (so you can easily get other adapters - indeed, standalone, it happily connects to my colleagues Sharp Zaurus).
The price? £4.99 from GPSForLess. A bargain in my opinion.
The loox adapter is a 'copy' of the standard one you get with the device. If you want to buy an original adapter replacement, it'll cost you £6.99! You're better off buying the power supply - it seems that more is less!
Anyway, I'm rapidly slipping off topic, so I'll shut up now and go off to my metting for which I am now late!
There's dedication for you!
A.