In my SVN repository tags are listed by version where name contains dots. e.g. 0.10 or 0.12.1
branches are named like proj-0.24-rc
In the same time, for example in Mono project branches has not dots.
Is it some practice to avoid dots? Could it be treated like extension delimiter (by web server where repository is been served), etc?
I think many large projects create tags with dots/periods, so I don't think there is anything wrong with it (at least not from a Subversion standpoint).
If you have some special software that is being thrown off by the periods... Then I guess that is another story.
There certainly is not a technical limitation.
I have been using dots for branch and tag names for ages and never encountered any problems with any of the SVN clients I have used.
Watch out for SVN identifiers which make problems on some platforms. For example, Windows can't deal with names only differing in capitalization. Also certain characters (:, /, \ etc.) are reserved on certain platforms and shouldn't be used.
I'm not aware of any platform... well, besides CPM or DOS, that is, so let's say: I'm not aware of any relevant platform having trouble with arbitrary dots in file system identifiers, so I think these are not a problem.