[PeterThaGreat]

Originally Posted by Kalevi

There's very little preserved written documents concerning Finland from those ages, and so far as I know there's not any indication of Swedish immigration before Finland was annexed by Sweden starting from 1249. Being associated with an armed conquest is bad PR?

Atrociously false, pure arbitrary. Swedes have settled Finland since the Iron-age (1500BC) and proto Scandinavian languages have been spoken in the country through the Iron-and Bronze age, this can easily be backed by any recent genetical study on Finnish etnogenesis and by archelogical fact as well, these early arrivals were only finnicized and eventually adopted to Finnish language, however this group has left a significant impact on the genetic pool of contemporary Finns.

(Just a recent article in Finnish illustrating the topic by the emeritius professor of history of the university of Åbo)
Turun Sanomat

I don't know to which extent this has been researched, but so far as I know the Fennoman movement was not somehow exclusive to only those Swedish speakers who were aware that their ancestry (or part of it) had been Finnish speaking.

The Fennoman movement was orchestrated by large part by Fennoswedish scholars, it started first only as a sympathy for the underpriviledged folk but after the Finns accused the Fennoswedish of being of alien stock who should return to their original homeland, they quicly left the movement. However, many notable fennoswedish families adopted to Finnish language and even finnicized their names.

This sounds like an attempt to give the reader a picture of a straight-forward ethnogenesis that resulted in a distinct, uniform population. Genetics tells a different story: all estimations of Finnish ancestry in modern Swedish speakers that I have seen have given results ranging from a little more than 50% to 75-80%. These kind of studies are however quite dependent on the Finnish speaking reference population. The more recent population developments in Sweden may also have some influence.

or 0%, I can post some studies form you are interested.
Stay out from the genetics not your sharpest tool. The fact is that genetical affinities can only be reliably tested by genomine DNA studies and so far Fennoswedes have not been sampled. Most Fennoswedes are descended from Central-Swedish settlers, particularly from Helsingland. Fennoswedes have Finnish admixture in varying degree depending on a region (close to zero in Alanders, little in the rural coastal dwellers, pretty much in the city bourgoise) due to the fact that there's always been Finnish chicks involved to some extent, however I don't see this as a prove of heterogenenity, the overwhelming majority of Fennoswedes live in a very uniform culture, whether they had some additional Finnish or German influence. Also, remember Fennoswede in racial context is only a person born the Fennoswedish parents, not to a parent.