It's very hard to get a proper fix on EGNOS unless you have a.) specialist equipment (at the moment) and b.) a clear line of site to the horizon in the east.
All sorts of other variables, like your location and if your too far north it will be difficult to pick up any signal properly.
I believe that some people have had success with handheld devices and managed to get a fix with rough indications of accuracy to within 3-5ft which is bl**dy good. Personally I haven't managed to get a fix on mine yet as it needs half an hour of clear horizon view to download the data for positioning.
Once you have the data (Almanac I think it's called) it doesn't need to download fully again but will receive updates. Until I know for sure that it's on I've turned my WAAS (EGNOS....but same difference as uses the same frequencies as in the USA) off as you lose 2 GPS satellite positions whilst it try's to find the EGNOS satellites.
On a good day I get 3m accuracy with EGNOS turned off and then 8m with it turned on but no fix on the EGNOS satellites. So you see it is worth turning it off until you know what the crack is and when it's turned on properly.
They are going to launch at some point this year for non-essential and non-lifesaving situations and are warning that you mustn't rely on it for such instances......I assume that's stop anyone in an accident trying to sue the pants off them.
I would assume that even when it's launched in test phase you will get a noticable improvement in signal quality and whether you will notice any improvements in plotting and navigation it is probably doubtful; or at least general navigation from A-B.
The main benefit I can see is "close in work" i.e. in shallow water, close to rocks or are looking for something in particular.... i.e. a wreck to dive on.
Tricky, close in navigation in areas you are not accustomed to I would still double check with an admiralty chart and not rely solely on your chart plotter but then I'm old school and have grown up with charts. I was quite suprised the other day when out on a very low tide that a couple of rocks appeared that I thought were covered at all times.....you can never be too careful!!
As with EGNOS a brilliant show of European project management, beurocracy, tea breaks and siestas! Well done Europe another masterstroke from start to.......well not even finished!