The original memory sticks in my late 05 G5 recently failed, but it was easy enough to re-upgrade. Every Apple/Mac I have from all the way back to 87 still runs as it was designed, especially the G5. It is a bit loud sometimes under load, especially compared to my Mac Pro, but it's really a monster that was way ahead of its time.
They're a bit power hungry, so you might want to consider that if you plan to run your G5s 24/7. I do run my G5 24/7, headless, and it consumes roughly 180W-230W at any given time depending on how many AppleTVs or time machine backups are running to it. It handles everything I can throw at it.