We've had ours just over 2 years and it's only just starting to look a little grubby in places and that's with 2 DSs and a less than clean DH. I'm really hapy with it. Just would prefer not to pay £££s to have all the covers cleaned. I may experiment on some of the scatter cushion covers.
I have an IKEA sofa, not the same one, with removable covers and I've washed them about a dozen times. Last time the zip broke on one of the scatter cushion covers but generally the only problem I've had is that it made the rest of the sofa look filthy!
I've got that sofa and had to wash the covers recently due to a child vomit incident - chickened out of the washing machine though and had them dry cleaned. They came up like new, although a bit of a squeeze to get cushions back in. Think I made the right choice as am sure they would shrink more in the wm.
If you do decide to chance it in the wm, can you update with the results please? so I can get the other side the same colour