Depends on the browser really. Last I checked, which admittedly was a very long time ago, Microsoft still was using individual files for each history entry, same as favorites. I know Firefox migrated to putting everything into a database a long time ago, so in theory it's limit is the limit of that embedded database program, which is probably in the millions of records on the average computer. I have absolutely no idea how Chrome stores these things.
The practical limit depends on how each browser stores this info and then the resources of your computer like CPU power and RAM. If you're using a rather inefficient method like Microsoft, after probably a couple thousand entries you'll start noticing significant performance hits on anything related to the history because of all the overhead associated with reading in each individual file. Firefox will likely keep chugging along quite happily, with no noticeable performance degradation for quite some time. Assuming Chrome does something similar to Firefox, which would stand to reason since Google hires engineers and basically lets them design the best software they can, it too would be able to go for some time without any noticeable performance hit. But of course even the most well optimized database has its limits. If you've got, say 4GB of RAM on your computer and your database is 6GB in size, you've got a performance problem. Plus it still takes CPU cycles to sift through all that data.
Does anyone know if there is a practical limit to the number of days IE, Mozilla, Google Chrome etc will actually save browser histories? For example I know I can set each browser to save histories for 365 days, but will they in fact do so?
Also, can anyone recommend any software which displays browser histories from all browsers by date and subject in a user-friendly way?