Depends on what distances you are driving and on what roads. Mythbusters did a program which involved "Drafting" (or "Tailgating" for us UK people) a "Big Rig" ... they noticed a huge percentage fuel economy gain as distance decrerased ... 20 feet spacing @55 MPH (Lorries in the UK are limited to 56 MPH) = 27% fuel economy increase (but also equals more risk to you if they breask hard).
I have tried this on a trip to my Girlfriend's, which is 126 miles away on mostly dual carriageways. I also increased my tyre pressure from the recommended 28 PSI to 30 PSI (another "fuel saving" tip). On the way there I drove very calmly, and only overtook a lorry when a big van went past, or even better, stuck myself behind a coach (they are limited to 65 MPH).
On the way home a few days later, I tried to stay clear of lorries and drive the same way (slow acceleration), but avoided tailgating lorries and stuck to the speed limits. The tyres were still at 30 PSI and it was chucking it down with rain most of the way home (which was quite scarey in some places as higher tyre pressure = less grip!!!).
After I got home I figured out that my fuel usage on the way down compared to the way home was practically identical ... kind of throwing a spanner in the works of the Mythbusters findings
You can watch the American version of the Mythbusters clip here:
(took me a while to find it)
However, I would suggest chucking a couple of doses of Redex into your system and avoid supermarket fuels, as that did help my first Hyundai's fuel usage change from about 230 miles to a tank upto a maximum of 320 miles per tank (only had a 45 litre tank - and was rated in distance from full until the empty light stayed on all the time).