I'll try to tackle this question.
As a former Wall St slave, I've seen many investment bank professionals jump from one job to another. Usually, the trend is like this....
1) Get a job with big name IB right out of college
2) Put in few years in - however, depending on your expertise/area and job market demand, many former colleagues left their respective positions even after just one year. (mainly due to headhunters calling from all over the place)
3) After few years, many return to bschool. Others jump to more lucrative positions at other firms. Many Wall St big name banks don't like newly hired employees from competitors. (i.e. - GS employee jumping to Morgan Stanley and vice versa - mainly due to culture clash) Most people choose hedge funds, and boutique firms after a stint at big banks. (easiest to get in and great bonus....sometimes less hours) PE and VC firms are little more difficult. One needs to have a fantastic network/contacts or resume. However, nothing is out of the question.
4) MC to IB/Wall St or Vice Versa - This switch is seen more frequently after bschool. Mainly because MBAs get recruited into direct training programs and that makes transition easier. However, IB/Wall St professionals usually jump at opportunities to open their own shop or any other option that will give them equity/capital. This is because many already devoted countless hours working like slaves. They want to cash out and run their own show. Many stars of IB usually take this road because due to their star status/reputation, they can find investors easier. For former MC's, some do enter Wall St/IB but many choose PE, VC, Start-ups and other consulting gigs. PEs and VCs actively recruit former big name MCs and offer more money. Many end up at D.C. lobbying gigs or start-ups because compensation can be anywhere in mid to upper six-figures to seven figures.
In conclusion, exit opportunities are usually unique, but in many ways abundant for former MC and IBers.
Of course the state of the economy affects the number of opportunities - but the opportunities are there.
Former IB/Wall St warriors often don't choose the corporate route. They have high expectation for compensation and etc. Also, many corporations prefer hiring accountants (many number crunchers on Wall St don't know how to close books every month etc - this task is usually reserved for back office operations ppl) or people out of their own finance development program.
Former MC's have more broad options in my opinion. Mainly because their critical thinking skills can be used in just about any industry. Also, once you go through few years at top consulting firms - you are specifically trained to think/work in certain ways. (although recently, there was a study of how former MC'ers make poor CEOs or top executives.....)
Important thing is to establish great contacts/networks as well as his/her reputation while slaving themselves in big firms.
Most current IB and MC'ers dream about their next career when they leave their current respective positions. It is important to have allies everywhere because that's where you usually find your next opportunity.