I am using a phone charge and have had my Pi turned on and acting as a 24/7 web host, torrent client/server, mumble server, ftp server, and SSH proxy, the only times it's been turned off is to reboot it after a firmware upgrade or because I'm too much of a noob to remember the command to type to restart a service so I just reboot the Pi.
It's also running a good but not overly stressful 850Mhz clock on it.
Remember, this is the same SoC that phones use, and you would be a little bit annoyed if your phone came with instructions saying you can only just it an hour a day
There are things you can do to minimize the SDCard writes because as you say, they will eventually wear out. I forget the name of the software (ZRam rings a bell but don't quote me on that) that stores all logs in RAM and only does an hourly dump from RAM to the SD card rather than loads of writes a second for all the services. I believe thats how it works, I should go and read up on it again but I hope you get the idea