I used this technique very effectively in the past achieving multiple listings on the first page, one from main domain and other sub-domains.
Not that it matters much if at all but this practice was great for building up page ranks (page rank sculpting). It allowed me to have a homepage of 7 with all but one of 12 sub-domains with a page rank of 6 and one with a 5.
That being said, this was years ago and it was a website with tons and tons of unique content (as I’m sure you can imagine with 12 sub-domains).
I think this method can still be helpful but you have to remember that a sub-domain should have enough content etc to be its on website (in order to not recieve negative impact) otherwise don’t create them. If you do choose to go ahead I would suggest starting with a couple at first at most and see how it goes before rolling out 5 sub-domains and loose search rankings. Also, remember to include text based links to the sub-domains (at least at first) from your main home page (I had success creating a text based sidebar listing all sub-domains using my top desired keyword phrases as the anchor text).