Cool app, but would need some more features to be actually useful. Here's my wishlist:
(1) Show line number next to buses and trams. (2) Option to disable auto-centering to GPS location (to demo the app to someone while in suburbs). (3) Line selection, show only specific line. (4) Draw the route of selected line to the map. (5) Quick button to open reittiopas.fi in browser with current location pre-filled. (6) More bus lines (but I guess that's not up to you).

Henri, indeed, I could see the trams in Helsinki, but not Busses so far. I haves asked HSL about the plans to provide the GEO position for more lines.
As a suggestion, what about showing some icon in the middle of the map (own position). I was also thinking, if it would make sens to let the user choose whter he/she is in a bus or tram, type the line no and publish the geo position for other users. Too bad that this would require an extra server component :/