I think you'll like it

Please see the update at the bottom of this review. -m

We picked up the 305 for a couple reasons: (1) my trusty old Timex Ironman Speed + Distance system finally died on me, and (2) as one of us is an expectant mother, we wanted something to track heart rate during workouts (primarily running). We've been using it for a bit more than a month now.

Overall, we couldn't be more happy with the 305. I'm used to running with a GPS, and it has all the features you would normally want: speed, pace, distance, alerts, laps, on and on... Distance measurement is pretty accurate (usually within 10 - 20 meters), and the reception is great (even under pretty heavy canopy on trails!).

The cool stuff:
* Enter in your date of birth & weight and it sets up heart rate zones for you. Calories burned are also calculated during your run. There's even a feature to enter weight for extra gear (if you're wearing any) to make the caloric computation include that.
* Alerts/alarms -- you can set these to go off based on distance (every mile or so), time, reaching min/max heart rate, or reaching min/max pace.
* Autolap -- set it to record a new lap based on distance (every mile/km or so), location (passing your starting point), or when you actually press the lap button (of course).
* User programmable information screens. You get to have a say in what information is displayed during your event! (you can even have it show sunrise/sunset times)
* You can run with a computer generated "training partner" on your system. Just enter in the details for the workout you want & you'll see two little figures pop up on your screen (one for you & one for your "partner". A cute little graphic way to push you on your run if you don't have a real partner with whom to train.
* You can record data under three different "activity" categories: running biking, and other. Switching between the activities is a breeze on the fly (e.g., if you are participating in a triathlon).

A little more detail:
* Satellite acquisition is fast (especially in relation to my old Timex).
* As stated earlier, the unit has good reception, even under pretty heavy canopy or on overcast days, something in which my old Timex didn't fair to well.
* The heart rate monitor works well. We have never "lost signal". Simply wet the contacts before you head out and you're good to go.

The down side:
* This point is now moot. Please see the update below. If you are a Mac OS user, there is no native software support for the Garmin Training Center software (yet). This is coming this year according to a press release made by Garmin back in January 06. That said, there is a safari plugin for the motionbased website (Garmin support training site) which will upload your runs from the unit to the site (via your Mac), allowing you to see charts on info like heart rate, pace, etc. The plugin is still in beta release (i.e., not 100% ready) but it has most of the functionality we would want. They are actively developing for the Mac and improving the software with time. For me, the software is a bonus, my old Timex had no way to download runs to the computer, so being able to see our training on the web is great.
* Some may expect 100% accuracy on things like distance, elevation, calories burned, etc. Those who know GPS technology, know that you won't get that (especially in a small consumer electronic device). The same is true for the 305. The elevation/grade calculations for our runs are a bit off (but really close sometimes), and the distances don't always agree with what we know (for known-distance courses), but IMO the variances are more than acceptable for a small training aid like the 305. It is more accurate then my old Timex. (Ok, not a "downside" but thought I'd touch on it here...)
* Some folks have been complaining that the gold contacts (for the USB cradle) on the unit start to corrode after use (even one run). We have not experienced this at all. Rumor has it that upgrading to the latest firmware solves the problem (which we have done). Something about the contacts being left in the "on" position for communication even after upload to your computer is complete.

In the end... we are very pleased with the 305. It records our training accurately, is small and light, has plenty of "bells & whistles", and provides a good deal of analysis on what you really did out there when you hit the trail.

Update as of 1/28/07: Garmin has released its Training Center software for Mac OSX. It requires an Intel or G3 Mac running OSX 10.4. Now you can import your runs directly into Mac. You also have the ability to create & upload workouts to the device (as with the Windoze based software). At first flush, it appears that most all functionality of the windows version is included in the Mac version. Though slightly late in terms of delivery, Garmin held true to their word & provided a full featured product for the Mac. Free Download is available on the Garmin website, just click on the link for "Garmin Training Center" on the product page for the 305. The only thing that remains to be seen is a Mac based firmware upgrade utility. Lets see what happens the next time they upgrade firmware. Otherwise, you'll still need a windows box to handle that.

Additional info: Have been using this now for about nine months now. Still love it. Garmin has continued to release firmware upgrades & software updates to improve performance & accuracy. This continued development is nice to see.

In terms of satellite tracking, I have lost reception a few times on overcast days while under pretty heavy canopy. However, the unit recovers very quickly when patches of sky can be seen through the trees. This has improved with some of the latest firmware upgrades.

In the end, I still strongly recommend the 305. I've been very happy with it. Happy Trails!