Comment used to do about 100:1, but data is more important (Score 1) 414
It does not seem widely off - I used to manage a team of 10 people who did the admin/networking for 8000 users. We did not do all of the end user hand holding, though some days it seemed like we did. Our ratio was about 1:1 users to computers, so your needs may be higher with the larger percentage of users.
Rules of thumb are useful, but in any support function is it really important to keep data on what you are doing. If the team works really hard it seems like you aren't even there. Most people don't understand the "magic" required to keep this stuff working. If you track calls/time, it is much easier to ask for more resources/staff when they are needed.