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Any positive side effect?
I'm not seeing any blue.
Public maps will be included in the search results on Google Maps and Earth.
I didn't see that happen at all. However a see many listings made not for the business owners but for well known sites or companies (can't mention any here due to TOS right?)
It's not a language problem because happens the same on several languages. So I'd say including your blue icons on your maps is a waste of time. I wonder how those big companies made to list those business. Perhaps Google gave them a special access?
However, the best is to create a Google account and then upload these files as a custom map. If you do it and a lot (or add a lot of info) for a specific place/location, your maps can get featured when people searches for that specific location, driving some traffic (a lot depending on the place). Also your user gets featured too (as a top contributor), which helps a bit.
Note: do not hold your breath, Google Maps takes a lot of time for updating this, you may have to wait up to 3 or 5 months until you see an update.
//edit for a small correction (show instead of search)
Do you see google maps as referrers in your sites with any incidence?
Also, if you can embed your map in a website (important: embed the map listed in your google account), much better. More map views seems to help, but this is maybe just a noise signal.
Let's make it simple: go and search for a few of your favourite location in Google Maps. Probably you end up seing from 1 to 4 "top contributors" and above this some recommended maps. Just try to be one of those ;) Do something is useful and promote it.
This won't drive you a lot of sales, but will help you getting noticed on broad keyword searches and give you some visits, which is not that bad right?
And yes, is not a lot, but I a have a few referers every day from my custom maps. And not only to my site: they also click on the affiliate links I put inside.
Then it's up to you how you manage it and if you use it to drive traffic or not. In my niche it's not that difficult.
BTW: in my niche, it's easy to get a feed with thousand of locations. I always add information that no other one does, but you can get the same result withouth adding that info.
Anyway, my approach is always the same: if there's anything coming up that looks to stay for a long a time and being used by users, then you have to be listed there. If you can be of the first ones: I have arrived too late too many time... that won't happen again.