Hey Spike, I have a Logitech Harmony 525.
I bought the Harmony after getting sick of having just 3 remotes to shuffle controlling 4 pieces of kit. The reason I chose Harmony was because they were relatively cheap. Even cheaper nowadays (from ~$75). I base my comments on the 520/525 models as these are very similar (with the 360 being closely related).
BUTTONS:The buttons on the Harmony are mostly soft rubber with symbols printed on so they will wear off after much use. There are a couple of hard plastic buttons on and around the central navigation control. The feeling you get when you press the buttons isn't one of quality, and they produce a creaky/clicky sound when depressed.
The layout again on the 525 is OK, though placement of the coloured keys on the bottom is a negative in my view because some of my gear uses these in various menus (BW PVR, Panasonic Plasma). The better placement is in the middle similar to the 360 and 785.
LCD SCREENThe 525 supports 4 "soft" buttons per page on the LCD and the screen is not colour. The 785 has a colour screen which supports 6 "soft" keys per page as well as icons eg favourite channel logos for Foxtel
You can assign just about any command to any button, and if the hard button is not present on the Harmony, you can virtuailise it on the LCD screen. You can also reorder/delete commands on the LCD so you only have the most often used commands on the LCD, but if you want to have them all there, you can have pages and pages of commands.
BATTERY LIFE:The 525 uses standard AA batteries which last about 4 months at a time. I use rechargeables which last about 3 months between charges. The higher end models use a rechargeable battery and come supplied with a recharger cradle.
SOFTWARE/DATABASE:The Harmony software is getting easier to use each time they upgrade it, but, it can be daunting for new comers and a little confusing. Once you get a small understanding of the principle of how the remotes work, then it becomes all the more easy to setup. You can add numerous devices to your setup, and not necessarily AV gear either....heaters, ACs, lights, blinds, cameras...basically anything with an IR remote. Of all my gear, I have found that the default setting for the device supports about 95% of the commands of the original remote, so usually, there's a couple that I have had to learn using the learning port...very easy to use.
There's also some support for discrete codes, so changing inputs, the Harmony can go direct to that input rather than cycling through a menu.
If upgrading models, the database can replicate your settings from your previous Harmony remote to the new one, so you don't have to set it all up again.
MACROS:The ability to create macros to control various equipment for each activity and keep a track of what's on and what's not when switching activities is a big plus for the Harmony. I presume the Prontos do this as well but I have no experience with them.
Once you set up your activities, you should not need to go into "Device" mode again, except for a command you don't often use. By keeping things in an "Activity", the devices stay in sync and the remote knows what devices are on/off and which inputs are being used. If you happen to get out of sync, a couple of presses of the "Help" key and things will be back in sync again.
You can also run "sequences" (mini single button macros) which contain up to 6 commands from a press of one key. EG you could programme in 0,7,0 into the "7" key so that when you press "7" while watching TV, it changes the channel to 7HD.
SUPPORT:Logitech's support line is very good, 7 days a week from memory, both phone or email, but phone is much better and quicker turnaround.
What the Harmony won't do is control a PS3 (it uses bluetooth technology) and RF controlled equipment, unless you import US RF models.
BUILD QUALITY:The general build quality is fair, and mine is going strong after several drops from ~1m height onto a wooden floor by the kids. By all accounts the Harmony's are not as robust as the Prontos, but for a starting price of $99.95 RRP, and the functionality they provide, I would buy another one in a heartbeat again.
CONCLUSION:Like anything I guess it's not perfect, but in summary, it's cheap and it's made our life a hell of a lot easier and enables us to use our gear more often because it simplifies things. The 5yo kids and Mrs diesel can use it and would be lost without it. Regardless of which brand/model you buy, as long as it can handle macros, it'll allow the Mrs to take back control of the living room and TV which...isn't such a good thing now that I come to think about it.....just kidding

. Get one, you won't regret it.