OK, I found how to turn them off in Pidgin: tools > plugins, then uncheck the libnotify popup box. For the Xfce power manager it's >preferences and uncheck the Show notifications to notify about the battery state box. Couldn't see any way to turn the Internet connection one off.
From some more googling it seems that notify-osd is responsible for these notification bubbles and you can disable them all by renaming the "/usr/share/dbus-1/services/org.freedesktop.Notifications.service" file (adding .disabled to the end was suggested)
Hope that might be of some use to anybody else that doesn't like them. I haven't tried to disable them all as the power manager and the chat ones were the only ones that were bothering me so I can't vouch for that method.
There's nothing particularly wrong with them but if you are having a discreet chat when you aren't supposed to be, the last thing you need is a huge bubble appearing with a message from somebody!
Thanks for your time again
EDIT: Should I change the title of the thread to solved or would it be better for me to try changing that file name and testing it first? (Perhaps nobody's really interested lol)
EDIT2: Well, as I've got nothing better to do, I renamed the file as suggested and after a reboot it worked. At least I'm happy