This is what I do:
If a system/forum etc "requires" a profile to be filled out and I dont want to provide personal information I either enter relatively generic information (i.e. "England" or County name rather than a specific town/village location or I enter a X or a TBA (to be advised) in the field. If a profile insists on a postcode and I dont want to use mine, I use the address/post code of a local post office or a generic postcode i.e. BT1 1AA, or G1 1AA and so on. If the website insists on a mobile number as part of the setup, I tend use the first 5 genuine digists and then 6 numbers i.e. 07711123456. I also never use a partial or full real name on any public facing fora I use.
At least it stops any nagging screens and means I have not shared any personal information with the greater world. I also tend to run two or three email addresses, keeping important stuff (i.e. online banking etc.,) seperate from general browsing. Hope this helps.