The answer to this really depends on the content of your thesis however, for the majority of people the answer is "Yes".

The reasons for this are:

1. Most people know how to use MS Word

2. The majority of supervisors use Word so there will be no compatibility issues when sending your documents through

3. It's relatively easy to find help if required

If you are in the Mathematics, Statistics or Computer Science field, you may want to look at another application called 'LaTeX'. Useful information can be found on the Wikipedia entry for LaTeX.