Q1:  Is there a C++ wrapper for GMP?

A1: Yes, beginning with GMP 4.0 one is bundled with the release.

Q2: When will the next release happen?

A2: See Future releases below.
    http://www.swox.com/gmp/#FUTURE

Q3: I get a segfault in a program that uses GMP to calculate numbers with several hundred thousand digits. Why?

A3: Upgrade to GMP 4.2. (Previous version of GMP allocated huge blocks of temporary memory on the stack, causing problems for some system.)

Q4: Are there known bugs in GMP?

A4: See under "Status ..." right below.
    http://www.swox.com/gmp/#STATUS