Personally, no, however I do have 100+ web sites all niche widget specific and this strategy works extremely well so long as your sites are not simply repeats of one another.
If you are building 25 sites under the same "corporate" style with a different subject matter for each site then this could work extremely well. By this I mean, for example:
site 1: general health
site 2: cancers
site 3: dentistry etc etc
You can interlink all of your sites without fear, despite what some may say, and you will probably find it much easier to control and also you can experiment with different ideas on each site to see which works best.
For everyone's information questioning this strategy I can tell you that some of my smaller niche sites with only 20 pages or so have the most incredible CTR's, 20%+, and eCPM's, some up to USD90.00+, and the EPC's average much higher than the larger sites even though they are ostensibly all carrying the same ads.
Obviously your biggest problem is going to be optimisation and getting good SE rankings since there are a plethora of health related sites therefore my biggest question would be "Where are you going to find enough unique content to justify good rankings etc for these subjects?"