I'm rather late replying to this thread but it came up in a Google search.
What's been said in this thread is very much the case, one persons allowance gives no indication of yours.
I for example was approved for 11.68kW (UK Power Networks), I initially applied for more and would of got that, but reconfigured my install. The reason I got so much, I live next to the substation, and we are the first house on the line, with many others, I don't think there is any other solar in our street either. That's ours now, and they can't take it away as far as I'm aware.
If you're in a town, and there is not much solar around you, then you are likely to get a higher export limit, if on the other hand, you are in the middle of nowhere, and very few neighbours, then you will only be allowed to export 3.68kW - this you are legally entitled to export. If you wanted to export more then the DNO will give you a price for upgrading the network to cope with it.
Is it worth exporting, absolutely, last year on Flux our export earnings alone was £1636, factor in everything (FITS payments at 2015 rate, 1 referral, saving sessions, gas, electric) and our energy bill was -£406.
This year won't be quite so good as rates have dropped, I currently get 15p and 26p per kWh, our April energy bill was -£10, thats gas and electric.