does anyone know what the limit is to the number of values you can add to a smart list filter?
It is recommended to keep them under 100 items - Tips for Building Better Performing Smart Lists. Not sure if it fails after that, but this is generally the max number Marketo suggests.
The most I've had successfully is ~1000 in one filter, but that was just looking at a single field to contain any of those values. There is a hard cap that marketo will reject, and I know that number is somewhere less than 4000. Definitely wouldn't suggest trying anything that high either.
The filter choices is 2499, but he meant actual filters.
Number of values you can add to a smart list filter
That sounded to me like filter choices rather than number of filters. Either way, both are answered now.
While the theoretical limit is 100, it is a good idea to follow those suggestions. I rarely do more than 15 and don't recommend going beyond that.
Same with Choice Steps - more than 7 seems to seriously slow the UI.