I generally don't use my surname, O'Connor, on the internet, or with any computer system, as it seems to be too difficult for some computer systems and/or people.
Many computer systems have problems with the apostrophe in the name, less now than was the case when computers first started being used by banks and businesses, but it can still be a problem. In a previous job, where my surname was included in my email address, this address was sometimes rejected when I tried to subscribe to some mailing lists, or rejected by their internal system when someone tried to send me an email.
It never ceases to amaze me that the majority of people do not know how to spell O'Connor, even though it is a relatively common (sorry, I mean frequently used) name - this was more a problem in Canberra than anywhere else I've been, despite Canberra having a suburb with the same name and Canberrans being supposedly more highly educated than the rest of the country. People can get it wrong when they are copying from a correctly printed name in front of their eyes. Again, I have had people ring me saying my email address was incorrect, when it was actually they who had spelt it incorrectly. It is a simple name and it is not difficult to get it right. For those of you who are unsure, O'Connor does not have an 'e', it starts with a capital 'O' followed by an apostrophe (') and a capital 'C', and it has two 'n's.
I prefer people to NOT call me 'mister' or 'sir'. Doing so indicates that you think I'm better than you. To me, 'mister' and 'sir' are remnants of the master/servant English past. These were titles given to the privileged in society, used by the lower class. It's worst manifestation can be found in cricket in the old days (up to about the 1960s), where the amateurs, or gentlemen, were called 'mister' while the professionals, or players, were referred to only by name, their names were differentiated on the score sheets, they had separate dressing rooms and only a gentleman could become captain. I reject this form of segregation and discrimination, and consider all people to be equal. Australia is supposed to be an informal, classless society, where all people are treated fairly and equally. If I meet you, I will consider you to be my equal, I will call you by your first name, and expect you to treat me the same. As I usually say to people, my name is Don . . . or my name isDon.
Many, many years ago (about eight!), when I first became connected to the internet, I had to provide a user name, as we all do. The format recommended by my ISP was surname and initial. I didn't do this for the above reasons. The user name I first selected was 'Don', which was disallowed by the ISP as someone already had that as their user name (this person got very confused when he started getting emails from my netball team, but that's another story!). So I had to pick something different, and as my name is Don, it very easily became isDon. I've used this as my user name everywhere on the web that I've been able to (some sites require a longer name, and on some sites the name is already taken - there are others out there using my name!) and I've simply become used to using it.
So, when it became time to register my web site, I couldn't use O'Connor in the name because some computer systems would have difficulty with the apostrophe (I'm not sure that a web site can even be registered with an apostrophe in the name?), and because I couldn't rely on people remembering how to spell it - I don't want offers of work or requests for images to go missing just because someone can't spell my name. I'm used to using 'isdon' and it is easily remembered so it was the obvious choice.