Ron with IWC - I never let it re-seed on purpose. Whenever the field is more than 50% "in bloom" I mow it. It usually works out to 3 times a year - After the last mowing around Labor Day - some heads will always go to seed - but I'm not convinced that the natural seeding does much.
Ladino does a good job of "filling in" the field through propagation from the roots.

A good White Clover Plot (Like IWC) should stay REAL strong for 3 years - and decent another 2-3 years more with regular mowing. I've tried overseeding a couple times - but I've never been real pleased with the results - the truth is that the clover makes ALOT of nitrogen available for invading grasses - and they begin to outcompete the clover after three years. There are those that say you can extend the life of the plot by a couple years with a spray like Poast - and maybe so - but for what it costs - I'd rather plan on re-planting clover plots (or rotating them with other plots) every 4-5 years. Here's a picture of the last IWC plot I put in in 2000. some of you might recognize the picture for an old post. This was the plot's second year - and was very thick with clover - 1st mowing 6/22/02:



Here is a closeup picture of the same plot in June this past year - 2004.
There still is alot of clover - but grasses have really started to become a problem. Mowing helped - but 2005 will probably be the last year of this (my favorite) clover plot - then it will be corn.

For Red Clover - and Alsike - Alowing it to reseed naturally bewteen July 4th and the 1st frost is a good idea - Mow it when most of the seed heads go brown. These clovers are basically a 2 year Perenial - allowing them to go to seed seems to get you another year or two.

I've never done it - but I'd guess Annual clovers like Crimson clover - should be allowed to "go to seed" if you are not re-planting after the year.