The other poster pretty much summed up my experience also, although I've had the Hero since it came out. The MR (Maintenance Release) that came out a couple weeks ago cleared up most of the problems.
As with any smart phone, you are NOT going to get days of use from the phone, but I have never, ever in my life had a phone that could go much more than 24 hours between charges... I read some people talking about smart phones saying they "have to charge it every day!!!!" and I'm thinking to myself, "How often did you charge your last phone?"
I guess the fact I use my phones a LOT (2000-3000 minutes a month) and the fact I've had a Blackberry for the last 4 years that was also very battery hungry might cloud my opinion on the matter a little. I've always been in the habit of charging my phone every night, and having a car charger, since I never know when I'm going to end up in a 2 hour support phone call. The first few days when you get it and are trying out "everything" you'll end up with a dead battery, but once the newness wears off and you get into more of a routine with your phone, the battery should last you all day without any serious problems. You can always pick up a couple of spare batteries and an external charger for around $20 on ebay.
The lag issues generally happen when you have something open in the web browser that is constantly refreshing in the background. Get one of the "task killers" like Advanced Task Killer Free, and kill off the browser that is running in the background if you notice it getting laggy, that almost always solves the problem for me (not like it's a constant problem, anyway.)
The disappearing apps was certain paid apps not showing up in the app store, it was a Google/HTC problem that was resolved. Some people do report a dust problem. Almost everyone experiencing this problem carries the phone around in their pocket without a case, and the pocket lint is entering the phone somewhere. Also the issue of crashing with too many apps was mostly due to a bluetooth bug, and has been resolved with the MR. There is a limit to the number of installed apps, probably closer to 100 than 20, but if you root the phone (safe and simple) you can choose to install your apps to your SD card instead of the phone's internal memory which will resolve the issue. The entire problem of actually locking up the phone should be resolved with the release of Android 2.X promised by HTC in the "near future" (few weeks, month or 2, we don't know.)