Scala implicit usage choices

I've been wondering whether transparent implicit conversions are really such a good idea and whether it might actually be better to use implicits more, um, explicitly. For example, suppose I have a method which accepts a Date as a parameter and I have an implicit conversion which turns a String into a Date:

implicit def str2date(s: String) : Date = new SimpleDateFormat("yyyyMMdd").parse(s)

private def foo(d: Date)

Then obviously I can call this with a transparent implicit conversion:

foo("20090910")

Would it be better to make the fact that I am converting the string into a date more explicit?

class DateString(val s: String) { 
  def toDate : Date = new SimpleDateFormat("yyyyMMdd").parse(s) 
}

implicit def str2datestr(s: String) : DateString = new DateString(s)

So then the usage looks more like:

foo("20090910".toDate)

The advantage of this is that it is clearer later on what is happening - I've been caught out a few times now by transparent implicit conversions I should know about (Option to Iterable anyone?) and this usage still allows us to take advantage of the power of implicits.