I've had a garmin Etrex (RS232 interface, takes AA batteries) and it's noticeably bad in woodlands so I've been wanting to get a new GPS for ages.
Since my Pandora should be here soon i've been looking for a Bluetooth gps. I found the iBlue 747A+ on ebay and it's rather nice, if a bit of a fiddle to get working. The Usb interface is a bit off standard and corrupts data on win2k.
Here's an picture of the difference in accuracy compared to the Etrex:
Notice the track that zooms off the road down towards the bottom left and then sharply turns to rejoin the road - that's the etrex loosing lock in the wood, interpolating and then jumping back to the road when it regains a lock.
The other nice thing about the 747A+ is that you can specify how and when it should log - every n seconds or every n meters etc...