Depends what it is.

If it's work, appointments etc I'll get there on time or earlier.

If it's a social event with friends then I'm pretty lenient because I know most of them are pretty terrible timekeepers. Doesn't really bother me if someone is late - I won't grill them for the reason of it I'll just be happy they turned up. My time is no more valuable or important than anyone else in a social event unless we have something booked (i.e. restaurant table or cinema tickets) for a specific time.

What *really* irks me though is people who are all "yeah yeah yeah I'll go" and then never show up or get in touch with anyone about it. That I will grill them a bit on.