updating sitemaps - how often?

[iWebTrack]

Hello -
I am managing a e-commerce website, which has around 600.000 products to sell. I want to know how often we need to update sitemaps, should we do after we add/remove new products from our inventory or should we do that on a monthly basis for example?
Thanks in advance for the help

[toplisek]

Do this with software and automatic. Do not use your time with manually added links.

Maybe some will suggest the best software.

[iWebTrack]

I am using gsitecrawler for creating the sitemaps, but I want to know how often to crawl the site for new sitemaps. Usually takes 2 days to create the sitemap...that's why I want to know which way will be most painless.
Thanks

[getxmlsitemap]

"Maybe some will suggest the best software."

There are web-sites avaialble 'get xml sitemap' which generate xml sitemaps.

[phranque]

with 600,000 products, perhaps it would be better to create a script to generate the 12+ sitemaps from the product database instead of crawling the site.