Thanks guys, the: "Go to Navigation settings and find the Update/Import POI option" which I deducted after all the comments is what answers my question. I had a quick look at it an hour ago and indeed there's an option to update POI's via an SD card so first part is done.
Second thing is to find the POI's I'm actually interested in. Ideally I'd like to be able to find any small shop's/company's address (big ones are already included as stock) much as I can do via Google Search. I know this is impossible but at least to get close to that. I guess some searching on POI suppliers will help but if anyone has good suggestions on sources of such POI's they are welcome

I also saw the 10 category limitation. My question is if I search for a POI, belonging in a category that is currently un-checked will it show up in the results or not? If it does it's ok, I don't want to see everything on the map at all times but if not I guess I'd have to make sure which 10 categories are active every time depending on the POI I'm searching?
PS. Fredgroves posted at the same time as me and I guess that answers my last question. If it is in the system it will show up in search results regardless of whether its category is checked for showing or not, right?