Multi-Table Question

How many tables can a MySQL db handle? Would it severly degrade performance if there is perhaps 7,000 tables in one db, or 7,000 db with 7 tables in each? The problem I am having is whether or not to consider using multi table or multi-db for storing. I am planning to setup a service which requires 7 tables. 5 of the tables have on average, 1,000-2000 records. The other two tables contain log information which can surpass the 100k range easily. I have an idea to cut back though to just a few records. . . Anyway, I was considering that once the site takes off, I will have the dillema of whether to give each new user, their own db with the 7 tables, or append their username to the back of a table's name and stuff it in one MySQL db. If there is a limit on how many tables can be in one db, I can setup the script to hold x accounts per db, that is, if there is no problem in regards to the performance. Also, would the answer to the questions above be the same if I were to use an Oracle backend db system? Thanks for any insights you can give to me.