Indeed, and most of the time it will go fine.
But you don't keep an eye out to check they are indeed renewed when they should be?
That none have been fraudulently transferred away?
The more domains you have the bigger an overhead it becomes - I'm not talking when you have 10 or 20, thats just a tedious management issue.
But when you start having 100s of domains, you have to ask if some of them arent similar enough in theme that they can be combined, thus increasing the PR and decreasing the overhead, with the added bonus of reducing the overheads of managing the domains.
But it all comes down to the routines - I'm sure some of us are better than others at organising the little details of keeping on eye on these things
(What a tendencious way for me to start on a forum! Quite out of character! <g>)