are most polish last names tongue-twisters to non-polish types?
No, they're not, but when a foreigner (
without any basic knowledge of Polish, which is rather common in the world) sees a 10-15 letters long name s/he panics thinking it will be too hard to pronounce, then even very simple names (like for example Nowakowski - pronounced quite smoothly) scare the speaker.
Other thing is that people try to
apply their own language rules
for Polish spelling, or what is even worse -
English rules, this way with a name built of sounds common (or similar) in many popular languages, people make an useless hassle for themselves.
Let's take for example Polish "rz" and "ż" (pronounced like French and Portuguese "j" and similar to the English sound in the ending -sure in treasure, leisure etc.) - but most people will try to pronounce it as "r+z", "r" or "z".
Same with Polish "sz" (close to "sh" in English, "ch" in French, "sci" (without the "i") in Italian, "sch" in German) - many foreigners try to say it as 2 separate sounds (s+z) which is hardly doable.
or "drz" and "dż" - similar to English "j/g" (in John/George), French "dj" (maybe not an official sound, but even said as "d+j" is still close to Polish, besides most people heard of jazz music, so they know the sound), Italian "g" before "e/i" (gettare/giocare).
There are only a few sounds (soft consonants "ć", "ś", "ź", "dź" that may be problematic, because many people don't hear the difference in those pairs "ć-cz", "ś-sz", "ź-ż/rz", "dź=dż/drz"). Other serious trouble may be the consonant clusters, more common in Polish than in English (Szczakiel = sh + ch + akyel, but people try to make it harder, s+z+c+z - I couldn't pronounce it either :)
The fact that we use "w" for the sound represented with "v" in many languages creates another problem (at least not for the Germans who also chose "w" for the Latin "v").