Your partitioning is fine. And is ideal for a newbie or SOHO system.
The problem with mounting directories on dedicated partitions is that if your needs change it is far harder to change the partition size rather than if you had just put the whole file system on one partition.
On the other hand, dedicated partitions for certain file systems can make backing up easier. For example, you might want to backup /var and /home quite frequently as they are likely to change often.
Similarly, you might want to put /usr/local on a separate system and back it up reasonably often because it contains sotware that does not form a standard part of a distribution.
Some people might decide to put /usr on a separate partition and never back it up because they reckon they can install all the software from scratch easily if something goes wrong.
It can also be a good idea to put data that is updated often onto different partitions that are rarely updated because the more writes there are to disk the higher the chance of something going wrong, so /var and /home should sometimes be on their own partition(s) and a different one from /usr or /opt.
If you are running servers different considerations apply. If I was running a news server I'd certainly put /var/spool/news on its own partition and if I was running a mail server /var/mail (or /var/spool/mail) should be on its own.
It just depends on what you want to do, but your scheme is beautiful for its simplicity. There are a few more thoughts here: