I should state up front that I'd like any responses to this to be about the specific problem of synonyms being "wrong" - it's going to be tempting to veer from that track, hence the request to stay focused.
It seems that synonym (single words and phrases) identification is being experimented with to an extent which is causing relevancy issues (more than usual with synonyms).
Have you noticed a rise in the number of searches which highlight words that are not correct for the search you made?
I have tested the problem with thousands of phrases that are vertical specific (in 200 different verticals) and chosen ones which I have painstakingly hand verified for several indicators of specificity (to measure how "far" they are from each of the other phrases in the vertical).
My results show that Google appears to not understand that phrases within verticals can mean very different things and that these differences can even suggest a term is consumer as opposed to business targeted.
The problem seems to be at its worst when the phrase in question incorporates a word that describes the vertical and includes another word which is rarely found (1% to 5% of websites in vertical) which means 90%+ of websites in the vertical don't cover the subject/product/service. In this instance you often see wider phrases being matched against the search, and those "matches" are often very wrong - thus making the results poor.
To make matters worse, there are sites that have the specific phrase but Google is choosing a snippet which highlights the wrong phrase - so there's no hint which would allow someone to see that site is better in the snippet.
This is tricky without specific examples, here's what the phrases target.
"broad service (whole vertical) aimed at businesses"
"quite specific service (but popular in that sector) aimed at businesses"
"very specific service (rare in that sector) aimed at businesses"
"broad service (whole vertical) aimed at consumers"
"quite specific service (but popular in that sector) aimed at consumers"
"very specific service (rare in that sector) aimed at consumers"
Assume that the websites usually target either businesses or consumers but rarely both (10% target both).
The results of a fairly representative search show; on a search for "very specific service (rare in that sector) aimed at businesses":
1st and 3rd are "very specific service (rare in that sector) aimed at consumers" - which is of no use whatsoever, this has NO relation to the search.
6th, 9th and 10th are correct
2nd, 4th, 5th, 7th and 8th are
"broad service (whole vertical) aimed at businesses" which might offer the service because they do cover commercial services (but in reality none of the websites did).
That's pretty shocking, especially when I know that there are 8 websites that offer the service and cover the geography searched for - all 8 of those websites are in the Google index and none seem to be penalised (although none have strong link profiles, they are local business websites).
The Lesson to be Learned?
From an SEO perspective it's clear that you need to make sure the title of the page is going to show that specific service/products/subject as you cannot rely on the snippet (which is not in any way news, it's just getting even more important). This is only going to encourage more thin pages again if left as it is - Google needs to fix this issue, pronto.