My application makes heavy use of temp tables. Should I be creating temp tables as needed, or should I be using a permanent table over and over instead?

Assuming everything is the same, both tables will produce very similar access speeds. If your application makes heavy use of temp tables, you might consider using a permanent table for these reasons: 

• A regular table already exists. A temp table has to be created, which takes time and overhead. For example, if you need to create a temp table 500 times a day, obviously a permanent table would be more efficient.
• A regular table can have preexisting indexes, while a temp table does not, unless you add them, which takes more overhead. Yes, records may take a little longer to INSERT if a preexisting index exists, but overall, the overhead is less than having to INSERT your data into a temp table, and then add an index.
• A temp table, when used, has to be managed in the tempdb database, which is additional overhead as it is created, used, and deleted. A regular table already exists, and doesn't take any extra effort to manage.
• A permanent table acts more like a global temp table than a local temp table. This may or may not be to your advantage. But even if you want the advantages of a local temp table, a permanent table will still work if you include the necessary column to differentiate the rows of different users, and the appropriate code.

Each of these potential benefits of permanent tables over temp tables is small, but in some situations, can add up to big performance savings. The only way to know for sure in your situation is to try both options.