When developing against lists, column names with spaces can be rather annoying. Internally SharePoint encodes spaces with the characters '_x0020_'. This isn't the end of the world but is a bit of a pain when writing code that uses the column names. Over the past few months I have found that I got into the habit of always creating columns without the space, and then renaming them.
As an example if I wanted to create a column named 'Account Number' I would first name it 'AccountNumber'. The internal name is set only once and is based on what the column is called when it is created. After the initial creation I can then safely rename the column with the space and still reference it as 'AccountNumber'.
I have developed the same habit for naming lists. With lists I think it is even more important to not have spaces as you end up with urls that look like this: http://site/lists/my%20task%20list/allitems.aspx. This is not particularly nice to look at and may even cause problems for some search engines. This is also makes it hard to read the URL and ends up as a bit of an accessiblity negative.
You can use the exact same technique as described for naming columns.