There's no such thing as an ordinary PDA any more -- all the best ones have sat-nav built in. There are some ropey examples out there, but Acer seems to be getting the hang of combining a Pocket PC with GPS.
The key thing it's got right with the C510 is the integrated antenna -- some rivals have flip-out aerials, which make them a bit unwieldy. It's also small and pocketable, weighing just 122g.
The CoPilot 6 software does a good job of turning the PDA into a sat-nav, but despite its prowess, it can't hold a candle to a high-end, dedicated sat-nav like the Garmin nuvi 660.
Maps of the UK come pre-loaded on a 256MB SD card, and there are CDs full of maps of Europe for you to install later if you need them, although you'll want to buy a new SD card before doing it.
The PDA side of things is looked after by Microsoft's Windows Mobile 5, so you get all the usual Word, Excel and Internet browsing shenanigans, along with the usually excellent Activesync software, which does a great job of copying your contacts, tasks and emails from your PC.
If you need a new PDA, and you've been thinking about getting a sat-nav too, it's a solid choice. Expect to pay about £280. -JJ