I have "good use" of Si, the functions test told me so!
But seriously, I think my Si is strong because I have a good long term memory of the past. And I'm always noticing shit like when things don't match up to the way I'm accustomed to.
Oddly enough, I often find I'm better at recognizing changes in details than the details themselves. For example, if the carpet changes at my workplace I'll probably notice it right away but what I won't notice is the precise details of the pattern in the carpet (which I think is more Se).
Or I'll notice right away when driving that something might be wrong with my car because it driving it doesn't feel right even though I'd have a terrible time trying to articulate in words why the car feels funny but I *know* it feels different from what I've experienced driving in the past.
5w6 or 9w1 sp/so/sx, I think