Rizzla really depends on what sector of the market and area you are in. Can't say I have had any problems getting a tenant in any of my houses in the last year and there was only a week change over for both of them.
You also know it goes both ways just like landlords don't like bad tenants - tenants also don't like many landlords for various reasons. So if you find a good one it is best to stick to the relationship. But hey I guess some just like the hassle of moving!