I think what people are trying to say Frieder is design for yourself, what you think looks good. There are lots of gray scale skins out there, but it does not matter if they are old or new as long as they work on the operating system you are using, and you like them of course. I sometimes put out a new or updated skin every 2 weeks or so, but that's only because I have been doing this for around 18 years or so, and have tons of older skins I can update. If I start a new skin from scratch, it usually takes me a full two weeks or more to finish it, and as I am changing my design looks now probably longer. Maybe a new skin once a month or so. But it would not matter even if it was 6 months, if someone likes a design they will use it no matter how long it took the designer to create it.
P.S. A word of recommendation, you might want to work on the start button, it's a bit rough looking. Unless of course you want it that way.