The best thing about Mikko Hyppönen is no-one can spell his name the same way twice (including him - the rock and roll umlaut comes and goes). This makes him an absolutely awesome case for detecting people by name in text corpuses. Once you've solved it for Mikko, most other Western names present little in the way of issues.
Finnish people quite often find it easier to spell their name without the umlauts when appearing online. The situation used to be much worse when email headers and BBS usernames were still ASCII-only (before Unicode), but you still occasionally run into problems.
Most recently, I've had trouble using a street address with umlauts for Amazon AWS billing. Bad web apps tend to convert the umlauts into HTML entities and then recursively escape those entities with &s when editing data or resubmitting forms.
I was reading it as "Hyyppönen" until I read this comment and looked at it more carefully :P
Even though o and ö are not interchangeable in Finnish, I suppose just o is preferable to the "oe" abomination that is occasionally used. Especially if your name happens to be Töölö or something.
You may be describing the perceived effect of inconsistent spelling, but it must be noted that it is _not_ a "rock and roll umlaut". Ö is a letter separate from o; it is unlike German in which they are mere diacritics, or modifiers.
