It rather depends on your engine and what you're trying to tow with it.
If it's a petrol 2.0 (non-
) or lower and you're towing something like a 17 footer, then be prepared to struggle.
If it's one of the dCi's, then things should be better. Though some of the dCi's have relatively low outputs (as low as 95bhp) they should still out-torque most of the petrols through the useful rev range. If it's a 1.9 dCi 120 or 130, then don't worry - they tow like a dream. The 2.2 dCi will tow even better, though for some bizarre reason, the published weight limits are lower than for the 1.9. I imagine the new 2.0 dCi is pretty good (it's been set to replace the 2.2) though I've yet to hear from anyone who tows with one.
If you have the 2.0 petrol
you'll probably do okay, especially if it's the later 205bhp one. And the 3.0 V6 shouldn't struggle at all.
If you have a smaller caravan (our previous one was a 12 footer) then the 2 litre engines won't struggle at all. The smaller ones still might though.