I use 10w/40 in my car & have for 100k miles &
will continue to do so.
For TK's errr... spirited style of driving, the expensive alternative recommended
is Mobil 15w/50 as the vehicle sees alot of NS use.
for those using Mobil 1 15w50, why that instead of tws? TWS is thinner when cold, and thicker when hot, vs m1 15w50 (this was discussed on the e39 board, only reason was cost over there, but seems like TWS is the better oil)
For regular drive we use/advise Mobil 1 0W-40 (for example, excellent cold starts up on a S50, I don't want to imagine the thick oil in the vanos unit). For the ones that came off from TWS or want a higher viscousity because of the harder driving style / oil consumption we use Mobil 1 5W-50.