asterisk users - Apr 2004 - Asterisk: problems and good things

Hi,

I would like to use asterisk like a SIP-H.323 gateway where the SIP phones use
asterisk to makes calls too. I would use this on a quite big environment, and i
need some informations about this.
First i will like to know what do you think about asterisk. What are the good
things? what are the problems it has? 
I have heard that asterisk is not ok to use in a large environment. How many
concurrently calls can I have? How many SIP telephones can it stand?

My architecture is

SIP phones ----- H.323-SIP gateway/Asterisk ---- gatekeeer ---- H.323
softphones
                                                    |
                                                    |---PSTN gateway ---
phones.


Please you can tell me your experiences if you want.

Best Regards,

Mireia.