Due to the just-introduced Commercial Use Limit on Search, many LinkedIn members are hitting the search quota for the month in the first day or two of January 2015 - and have to wait another month to search again.
LinkedIn didn't say how many searches are "too many"; the experience shows it's around sixty searches for one month.
I find limiting the search for unpaid accounts reasonable. It's not new; a number of commercial search systems have similar limitations.
If you are struggling with the new limits on searching and are not ready to go with a paid account yet:
1) There are a number of ways to search that are not counted in the monthly quota. These ways are no substitute for the advanced member search, but can be quite useful.
2) Naturally, Googling for LinkedIn profiles ("X-Raying") remains unlimited!
Use this Custom Search Engine to X-Ray LinkedIn:
(I have updated the Search Engine URL to provide up to 1,000 results.)
Here are some example uses:
>> Let's connect on LinkedIn (I can't accept due to LinkedIn limitations but I will invite you back)
>> Follow me on Twitter: @braingain