Yes, I have done a masters - also part time - I think the total thing took me 4 years but I only did a reasearch report as I did half course work half research topic.
I was lucky that I had a topic to do stuff on from work. I also had the problem that my supervisor kept going overseas for weeks/months at a time so I would submit a version of my project only to have to wait forever to hear back from him. Lastly, after my project went to external examiners there was a big hooha cause they said they had seen the work before - obviosuly as it was for my work they had used it too. I had to get my managers to write a letter explaining that the work was something I did for them and had then submitted as a research topic.
I think if it weren't for all the hiccups and waiting around for people I would have finished in 2 years.
My previous masters was not in the IT field so I think that also plays a large role. Also, from the company I worked for, I had something like 25 years worth of data to use - I didn't have to go and make new data up or gather data - that also takes a long time - I know other people who started projects from scratch and it took them quite a long time to collect their data.
Celene