[Update: Format specifiers are not the same thing as format strings; a format specifier is a piece of a custom format string, where a format string is \
Label1.Text = dt.ToString("dd MMM yyyy | hh:mm | ff | zzz | zz | z");
will output:
07 Mai 2009 | 08:16 | 13 | +02:00 | +02 | +2
I'm in Denmark, my Offset from GMT is +2 hours, witch is correct.
if you need to get the CLIENT Offset, I recommend that you check a little trick that I did. The Page is in a Server in UK where GMT is +00:00 and, as you can see you will get your local GMT Offset.
Regarding you comment, I did:
DateTime dt1 = DateTime.Now;
DateTime dt2 = dt1.ToUniversalTime();
Label1.Text = dt1.ToString("dd MMM yyyy | hh:mm | ff | zzz | zz | z");
Label2.Text = dt2.ToString("dd MMM yyyy | hh:mm | FF | ZZZ | ZZ | Z");
and I get this:
07 Mai 2009 | 08:24 | 14 | +02:00 | +02 | +2
07 Mai 2009 | 06:24 | 14 | ZZZ | ZZ | Z
I get no Exception, just ... it does nothing with capital Z :(
I'm sorry, but am I missing something?
Reading carefully the MSDN on Custom Date and Time Format Strings
there is no support for uppercase 'Z'.