I also find the system sounds volume very low. I though it was low on the N900 and I missed quite a few calls because I did not hear the phone ringing in my pocket but Jolla's ringtones, SMS and email alerts are even quieter. Good job I do not use it as my main communication device.

They are also - at least the default ones - very short and rather unremarkable (for example, a simple "ding!" for an email alert). Fortunately that part can be solved by replacing the tones.