Depends what you leave on your phone in the first place, what unused apps.
I have deleted everything that I don't and never will use....Twitter, AIM, Yahoo messaging etc etc, and left on Facebook and things that I will use. I've not touched any of the Blackberry items.
I've deleted all the other languages except English that I use....this tip was from blackberry . com for freeing up memory, and this freed up about 30mb on it's own.
I started off with 34mb of free memory on the phone and now have over 80mbs free.
That's not counting what is on the sd card.
I'm not suggesting you blitz your phone, but it does rather make sense to get rid of stuff taking up memory that you don't use and make room for things you will use.
And I am a complete and utter novice so if I can do it anyone can...