CSS has been played competitively in SA ever since it came out, but for this season the league switched to 1.6 if I'm not mistaken. There is still some uncertainty regarding whether or not it will stay on 1.6 or if they will revert back to CSS after this season. If it doesn't I'm pretty sure another league will crop up, if you are into that sort of thing.
Unfortunately this also means that CSS servers are a bit more deserted now than usual. Of course, I still play everyday and there are still 3/4 servers filled each night (round 60-70 players). Not as much as about 2 years ago, but still great fun. There are also regular pickups if you're interested in that. All in all, the most active servers are IS and WAGE. No one plays SGS anymore because the lack of moderation. IS hosts 4 Dust2 servers, 2 Sniperless and 2 normal, and also one Dashur Pro server. WAGE hosts more casual servers, like Gun Game, Surf, BHop, Jailbreak, etc. The unfortunate thing is there are no more public servers with map cycles. This basically means you shouldn't expect to play the old classics (Italy, Nuke, Office, Assault etc) very often.
CSS is still definitely worth a buy through steam (+- R150). Add me on Steam if you have any more queries. ACC: Lo0nitic