I'm a member (for now). I work in leisure and fitness. I got in because I knew a load of people who were already members.
I go to Greek Street mostly, followed by Dean Street and the Farmhouse in Oxfordshire. I cannot bear Shoreditch House, although I go sometimes. I'm also a member of a couple of other clubs that aren't Soho House Group (it's useful for work).
It does err towards creative people but it's not a hard-and-fast prerequisite. The whole 'creative spirit' thing covers a lot of bases. To be honest, they'll be more interested in how often you're likely to be using the Houses, and also good-looking you are (yes, seriously).
I also know plenty of people who work in the City who are members and use it for social purposes in the evenings and at weekends. Money greases the wheels. So I wouldn't worry about not being a 'creative'.
Be aware that all the Houses feel oversubscribed these days. I frequently struggle to find a space at Dean, Greek or Shoreditch, even during the day. Summers in particular are a total pain. It can be very awkward if I'm trying to collaborate on something, arrange for other people to come, and then there's nowhere to sit. The other club that I'm a member of doesn't have this problem. I also find the competence of the staff to be on the low side. I had two guests left stranded at reception for almost 40 minutes not long ago because the staff had 'lost' the sign-in details and couldn't be bothered to call/go up to check.
For these reasons, and one or two others, I'll be cancelling my membership at the end of this year. So do check that you'll actually be able to use the Houses you want to go, at the times you want to go there IYSWIM. For me, it's no longer worth the membership cost.
I will miss the Farmhouse, that is genuinely brilliant.
Applications... it varies, I think. My membership went through fast, I found out within about a fortnight I think. That was a good few years ago now though.