Lion upgrade question

I'm new to the Mac world....

With all my windows computers, it was always better to do a clean install rather than upgrade each OS.

Is that the same for Macs? If it is will I need to have the DVD or can I still do a clean install with the download from the mac store?

Does anyone know how many systems you can put it on?

I'm trying to prepare for Lion

Thanks in advance...

Upgrade on a Mac is no problem.

You can install Lion on 5 computers.

Awesome! Thanks

Just be aware you do need to be running OS X.6.8 prior to downloading Lion, and it is very advisable to have the Snow Leopard DVD for troubleshooting etc.