Everyone I know with young children loves these places, but I must say that my experiences of them have not been all that great!
I never take my children to them, and never have although I suppose they are well past the peak age at which they are useful - ie - 7 and 5.
Today I went to one with a friend. Great I thought, lovely and clean (for a change!!) My friend informed me that many of these places smell of wee and poo because the children have accidents and nobody notices. My dd ended up hurting her wrist because she fell somewhere in the maze of stuff! (although in spite of this she wants to go again)
I don't know, to me they just seem so.....overrated. I would prefer to be somewhere else (especially for the cost as many of them are very expensive although the one today was not).
Perhaps soft play centres are just allergic to me and my children