It is a minefield for the poor end user who doesn't know a lamp from a bulb. Here goes;
GU10 lamps often come in 1000, 2000 and 5000 hour variations, you think you are getting a good deal buying from the supermarket or DIY shop but that is rarely the case, they are almost always the cheaper variants.
As someone has already said search out your local electrical wholesaler, ask him for some 5000 hour GU10 lamps. They will cost more but you will likely get the life out of them, however;
It also depends on what they are in and the ambient temperature the usually work in, also the amount of time you have them on. if they are in a Fire rated Down light they will have a higher 'ambient' temperature and will last a lot less time than in an open backed fitting.
Again as someone has mentioned, there are options. LED lamps are leading the way forward some of the bigger ones are 'almost' as good as GU10 Philips do a 7W 'master LED' (Sorry no link, the Philips website is a mare), Aurora do a 8.5W LEDzworld (link
Aurora - 'Passionate about Lighting' ). They are others, most claim about 30-50 hours life but they do cost quite a bit at the moment, the up side is that over their life span they will pay you back in electricity bill costs.
10 Gu10 50W lamps burning 351 days a year (counting for a few holidays) for an average 4 hours a day costing 8.5p per Kw/h will cost approx 59.67 a year to run .
the same in 8.5W LED lamps is only 10.14 !! (But the lamps cost a whole bunch more).
Think it through!
Enjoy.