Will it be much better?

The number of results will depend on the number of threads/posts on your forum. Approximately 400,000 indexed pages is pretty good. It's obvious that you have a highly active forum that has been online for quite some time (i.e. vB2.x).

You may notice that this number could get a bit lower. However, this is a good thing. vBSEO has many features designed to eliminate duplicate content, and we generally recommend that your archive link directly to the actual forum threads. During the early stages of installation, vBSEO will cause the search engines to purge much of your duplicate content.

Note: Our automatic 301 redirects will ensure that your currently indexed pages are updated within the search engines to the new CRU (content relevant URL) versions.

An even more important factor is that your pages will become more relevant for the keywords within the onpage text. So, vBSEO will not only help to get more of your pages indexed, but also helps to improve the average SERP positioning of each page for their most relevant keywords.

Hello Domenico, welcome to the boards

If you are willing to disclose your forum url, we might be able to make a better assessment.

My question is that I'm wondering when we upgrade and start using vBSEO this number will stay the same or will even get higher (or lower). What do you think? Is 399,000 (sometimes it is more) not already very high?

That will depend on the number of unique forum pages (forumdisplay, threads & posts) that are currently indexed and the way you set vBSEO.

As an example... lets say that you have 100 total postings in your forums, and you have enabled the showthread rewrites without rel=nofollows. You should expect 100 pages to be made more visible to SE's.

Example 2... if those 100 total postings reside in exactly 30 (1 page) threads, and you enable the priththread rewrite without rel=nofollows, you should expect these 30 pages to be made more visible to SE's. This is not recommended as printthread pages might be tagged as dup content.

RE: total number of pages... this might increase or decrease depending on how much dup content you have at present:

Example 3... If 50% of your current indexed pages are dup content, you should expect a decrease (over time) of 50% in content indexed. However, this won't be easy to track as many other pages will get indexed while the dups are being dropped . A good thing about it is that (in the process), all the ones being dropped are 301 redirected to the real, unique pages, therefore, helping you to consolidate that "scattered" relevancy.

yes - - for starters..

There is a PR split in your homepage:
http://www.webhostingtalk.nl/ PR4
http://www.webhostingtalk.nl/index.php PR2
http://www.webhostingtalk.nl/index.php? PR1

Dup content:
17K printthread pages

Noise content:
700 newreply pages
2.3K search pages
400 member.php pages

The above are examples, not comprehensive at all... Of course, this is only the tip of the iceburg - I will get together with Jonathan to post some sort of guideliness to help you guys analyze (expected) results better.

Cheers

that guideline would be nice ...